Syllabus
General methods of preparation, properties, reactions and uses.
ALCOHOLS, PHENOLS AND ETHERS:
Alcohols: Identification of primary, secondary and tertiary alcohols; mechanism of dehydration.
Phenols: Acidic nature, electrophilic substitution reactions: halogenation, nitration and sulphonation, Reimer - Tiemann reaction.
Ethers: Structure.
Aldehyde and Ketones: Nature of carbonyl group;
Nucleophilic addition to >C=O group, relative reactivities of aldehydes and ketones; Important reactions such as - Nucleophilic addition reactions (addition of HCN, NH3 and its derivatives), Grignard reagent; oxidation; reduction (Wolff Kishner and Clemmensen); acidity of ? - hydrogen, aldol condensation, Cannizzaro reaction, Haloform reaction; Chemical tests to distinguish between aldehydes and Ketones.
Carboxylic Acids: Acidic strength and factors affecting it.
-------------
Alcohols
Alcohols - Introduction
The hydroxy derivatives of aliphatic hydrocarbons are termed alcohols. They contain one or more hydroxyl (OH) groups.
Example:
Methyl Alcohol CH-3OH
Ehtyl alcohol C-2H-5OH also written as CH-3CH-2OH
Propyl alcohol C-3H-7OH also writtenas CH-3CH-2CH-2OH
They are classified according to the number of hydroxyl groups in the molecule.
One OH group in the molecule Monohydric alcohol
Two OH groups in the molecule Dihydric alcohol HOCH-2CH-2OH
Three OH groups in the molecule Trihydric alcohol
More than one OH group cannot be present on the same carbon atom. In such as a case, the compound will be extremely unstable and it will change into aldehyde. (This will be another topic in the syllabus itself)
Monohydric alcohols are further classified into Primary (1°), secondary(2°) and tertiary (3°) alcohols
Primary alcohols have one or none alkyl groups on the carbon bonded to -OH group.
secondary alcohols have two alkyl groups on the carbon bonded to -OH group.
Tertiary alcohols have three alkyl groups on the carbon bonded to -OH group.
IUPAC Nomenclature of Alcohols
Methanol
Ethanol
Propan-1-ol
Propan-2-ol
Butan-2-ol
2-Methylpropan-2-ol
Methods of Preparation of Alcohols
General Methods
1. preparation from haloalkanes
2. By reduction of aldehydes, ketones and esters
3. From Grignard reagents (RMgX)
4. By hydrolysis of eters
5. From alkenes
----a). hydration of alkenes
----b). Hydroboration oxidation reduction
----c). Oxymercuration - reduction
6. From aliphatic primary amines
Industrial Methods
1. Hydration of alkenes
2. Oxo Process
3. Fermentation of carbohydrates
4. manufacture of methanol
Physical Properties of alcohols
1. Physical state
2. solubility
3. Boiling points
4. Intoxicating effects
Chemical properties of alcohols
The reactions of alcohols are decribed under the following classification
A. Reactions involving cleavage of oxygen-hydrogen bond.
B. Reactions involving cleavage of carbon - oxygen bond
C. Reactions involving cleavage of both the alkyl and hydroxyl groups
A. Reactions involving cleavage of oxygen-hydrogen bond.
1. Reaction with active metals - acidic character
2. Reaction with metal hydrides
3. Reaction with carboxylic acids (esterification)
4. Reaction with grignard reagents.
5. Reaction with acyl chloride or acid anhydride
B. Reactions involving cleavage of carbon - oxygen bond
1. Reaction with hydrogen halides
2. Reaction with phosphorus halides
3. Reaction with thionyl chloride
C. Reactions involving cleavage of both the alkyl and hydroxyl groups
1. Acidic dehydration
2. Oxidation
3. dehydrogenation
Topics specifically highlighted in JEE syllabus
Esterification
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
The function of concentrated sulphuric acid is to act as protonating agent as well as a dehydrating agent.
RCOOH + HOR' ↔ RCOOR' + H2O with H2SO4 as catalyst
CH3COOH + HOC2H5 ↔ CH3COOC2H5 + H2O with H2SO4 as catalyst
The reaction is reversible is nature. Double headed arrow is used to indicate it. The equilibrium can be shifted toward the forward direction by removing water as soon as it is formed.
If dry HCL gas is used as a catalyst, the reaction is called Fisher=Speier esterification.
It is is difficult to prepare esters of tertiary alcohols becasue bulky groups in the alcohol decrease rate of reaction or esterification. This is termed as stearic hindrance of bulky groups.
As noted above in the reactions, esterification involved the cleavage of the O-H bonds of the alcohol. This was proved by using alcohol with isotopic O18 which can be tracked using isotopic tracer technique. It was found that this oxygen is present in the resulting ester which means that the oxygen in the alcohol is going into the ester and hydrogen is going into the water molecules.
Dehydration
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
Dehydration of alcohols to ethers or alkenes can also be brought about by passing the vapour of the alcohols over heated alumina catalyst under different conditions
Oxidation
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkalineor acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
Different classes of alcohols differ from each other in their ease of oxidation and also give different products.
(i) Primary alcohols: Primary alcohols are easily oxidized. First an aldehyde is formed and then from it carboxylic acid is formed. Both the aldehyde and the resulting acid contain the same number of carbon atoms as the starting alcohol.
(ii) Secondary alcohols: Ease of oxidation is still there. But they are oxidized to ketone and under strong conditions they are further oxidized to form a mixture of acids. While the ketone contains the same number of carbon atoms as the starting alcohol, the acids formed contain lesser number of carbon atoms.
(iii) It is difficult to oxidize tertiarly alcohols.
When treated with acidic oxidizing agents under very strong conditions they form first ketones and then acids.
Both the ketones and acids contain lesser number of carbon atoms than the starting alcohols.
Reaction with sodium
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas an form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to gibve Sodium ethoxide and hydrogen
This reaction shows that alcohols are acidic in nature.
The acidic nature is due to the presence of polar O-H bond.
Alcohols are weak acids even weaker than water.
Reaction with phosphorus halides
Phosphorus halides such as PCl5, Pcl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
Haloalkanes : Chloroethane, Bromoethane, Iodoethane
Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
Alcohols get converted into alkylhalides. As alkyl halides are insoluble in water, their presence is indicated by the appearance of turbidity in the reaction mixture.
The time required for the formation of alkyl halides and appearance of turbidity is very less in the tertiary alcohols.
in the case of secondary alcohols, it takes five minutes.
A primary alcohol produces turbidity only after heating.
Thus alcohols can be distinguished using Lucas test.
Conversion of alcohols into aldehydes and ketones
This topic was already covered in the topic of oxidation.
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
Phenols: http://aieee-chemistry.blogspot.com/2008/01/aieee-chemistry-unit-23b-phenols.html
Ether
http://aieee-chemistry.blogspot.com/2008/01/aieee-chemistry-unit-23c-ethers.html
Aldehyes and Ketones
http://aieee-chemistry.blogspot.com/2008/01/aieee-chemistry-unit-23d-aldehydes-and.html
Carboxylic Acid
http://aieee-chemistry.blogspot.com/2008/01/aieee-chemistry-unit-23e-carboxylic.html
Sunday, January 20, 2008
AIEEE Chemistry Unit 23B Phenols
Phenols: Introduction
Phenols are aromatic hydroxy compounds. In phenols, one or more hydroxyl group is directly attached to the aromatic (benzene) nucleus.
Phenols are also classified as monohydric, dihydric and trihydric or polyhydric as their molecules contain one, two, three or more OH groups.
Examples of Phenols
Monohydric
Phenol
2-Bromophenol
m-Cresol
p-Cresol
Dihydric
1,2-Dihydroxy benzene
Trihydric
1,2,3-Trihydroxy benzene
If OH group is not directly attached to be carbon atom in the benzene ring, but present in the molecule as a part of the alkyl side chain group, then the compound is not termed as phenol.
It is called aromatic alcohol because it resembles aliphatic alcohols in its characteristics.
Examples:
benzyl alcohol or Phenylmethanol
2-Phenylethanol
Nomenclature of Phenols
Common system
IUPAC system
All substituted phenols are named as derivatives of phenol.
The position of the substituents w.r.t.-OH group is indicated by Arabic numerals(with the carbon carrying-OH group being numbered 1).
Examples
2-Methyl phenol - Methyl group CH3 is present adjacent to OH group in phenol.
3-Methyl phenol - Methyl group CH3 is present in third position when OH group position is counted as 1 in phenol.
2-Bromophenol - Bromine is present adjacent to OH group in phenol.
--------------------
Phenols: Methods of Preparation
1. Alkali fusion of sodium benzene sulphonate
NaOH is fused with sodium benzene sulphonate at 573 - 623 K, sodium phenoxide is formed. This on acidification gives phenol.
2. From diazonium salts
An acqueous solution of benzene diazonium salt on warming gives phenol
3. By decarboxylation of sodium salt of salicyclic acid
Fusion of sodium salicylate with soda lime (NaOH and CaO mixture).
sodium phenoxide is formed. This on acidification gives phenol.
4. From Grignard reagent
when oxygen gas is bubbled through an ethereal solution of phenyl magnesium bromide (Grignard reagent RMgX), if forms an oxy compound which upon hydrolysis with dilute mineral acid gives phenol.
Commercial Preparation of Phenols
1. From chlorobenzene (Dow's Process)
Chlorobenzene is heated with 10% acqueous sodium hydroxide solution at about 623 K under 200 atmospheres andin the presence of copper salt acting as catalyst to form sodium phenoxide. The sodium salt when treated with dilute HCl, gives phenol.
2. From cumene
Air or oxygen is passed through a suspension of cumene in acqueous sodium carbonate solution in presence of cobalt or manganese naphthenate catalyst. The oxidation product is cumene hydroperoxide.
The hydroperoxide is then decomposed by hot dilute sulphuric acid when phenol is formed withliberation of acetone. Acetone is removed from phenol by distillation.
3. From Benzene (Raschig's method)
Vapours of HCl are passed over benzene at 500 K in the presence of copper chloride and excess of air to form chlorobenzene. Steam is then passed through chlorobenzene at 800 K in the presence of silica as catalyst to give phenol.
4. Phenol prepared using benzene and H2SO4
Benzene is heated with excess of concentrated sulphuric acid at about 388 K to give benzene sulphonic acid.
It is neutralized with sodium hydroxide solution, when sodium benzene sulphonate is obtained.
Dry sodium benzene sulphonate is next fused with excess of caustic soda at about 573 K when it yields sodium phenate (or sodium phenoxide).
Sodium phenate is decomposed by dilute sulphuric acid to give phenol.
Physical properties
1. State and smell: Phenols are colourless crystalline solids or liquids. They have characteristic phenolic odours.
2. solubility: Phenols are sparingly soluble in water
3. Boiling points: Higher than the boiling points of the aromatic hydrocarbons of comparable molecular masses.
BP of phenol (mol. mass = 94) is 455 K while that of toluene (mol mass = 92) is 384 K. This higher BP is due to intermolecular hydrogen bonding in phenols.
Chemical properties
Can be classified into three groups
A. Reactions of phenolic group (_OH group)
B. Reactions of benzene ring
C. Special reactions
A. Reactions of phenolic group (_OH group)
1. Action with zinc dust
2. Action with ammonia
3. Action with acid chlorides and acid anhydrides
4. Action with benzyl chloride
B. Reactions of benzene ring
1. Bromination
Action of Bromine water on phenol: When phenol is treated with bromine water, it gets decolourised giving a white precipitate of 2,4,6, tribromophenol.
Action of Bromine in CS-2 on phenol:o-Bromophenol + p-Bromophenol mixture is obtained. p-Bromophenol is the major product.
2. Nitration
Action of dilute nitirc acid on phenol: a mixture of o-nitrophenol and p-nitrophenol is formed.
Action of conc. nitric acid in the presence of conc. sulphuric acid on phenol: 2,4,6-trinitrophenol is formed. This is picric acid.
3. Nitrosation
The reaction which involves the substitution by nitroso grou (-NO) is called nitrosation.
Phenol reacts with nitrous acid (NaNO2 + HCl) at low temperature (280 K) to form p-nitrosophenol. It can be further oxidized with dil HNO3 to give p-nitrophenol.
4. Sulphonation: Covered as a special topic
5. Alkylation
Special reactions of Phenol
1. Kolbe's reaction: special topic
2. Reimer-Tiemann reaction: special topic
3. coupling reaction
4. Reaction with pthalic anhydride
5. Condensation with formaldehyde
6. Hydrogenation
7. Oxidation
8. Reaction with ferric chloride
9. Libermann's test
Acidity of Phenols
Phenols are weakly acidic in nature (Ka = 10^-10).
They turn blue litmus read and react with alkali metals and alkalies to form their salts.
The acidic character of phenol is due to polar OH bond.
Phenol is weaker acid than carboxylic acid.
Like carboxylic, it also does not react with sodium carbonate and sodium bicarbonate.
Phenols are more acidic than alcohols.
Phenol is a resonance hybrid of 5 structures. Three of the structures develop +charge on oxygen and facilitate release of H+.
Phenoxide ion which results when H+ is released from phenol is also a resonance hybrid but it is more stable than phenol. Hence the reaction is in favour of phenoxide ion. Therefore phenol is acidic and more acidic than alcohols.
Halogenation of Phenols (electrophylic substitution reaction)
The reaction does not require a lewis acid catalyst. Benzene requires a lewis acid catalyst for halogenation.
Bromine in CS2 reacts with phenol to give 4-Bromophenol(?)
Chlorine at high temperatures react with phenol to give 4-chlorophenol(?)
See http://clem.mscd.edu/~wiederm/oc2chp/oc2chpphenols/page3.htm
You can download a chapter on phenols from
http://www.diacritech.com/samples/science_and_medical/chemistry.pdf
Phenols are readily brominated in an aqueous solution forming 2, 4, 6-tribromophenol. This is a white precipitate.
Mostly p-bromophenol is obtained along with ortho bromophenol by treatment
of phenol with bromine in CCl4 or CS2.
Treatment of phenols with aqueous solutions of bromine results in replacement
of every hydrogen ortho or para to the -OH group. Bromination may
even cause displacement of certain other groups to yield tribromophenol.
Nitration of phenols
Action of dilute nitirc acid on phenol: a mixture of o-nitrophenol and p-nitrophenol is formed.
Action of conc. nitric acid in the presence of conc. sulphuric acid on phenol: 2,4,6-trinitrophenol is formed. This is picric acid.
Sulphonation
Action of conc. sulphuric acid at different temperatures on phenol:
Pheno reacts with conc. sulphuric acid to form a mixture of o-, and p-phenol sulphonic acid.
At low temperature about 288 to 293 K, o-phenol sulphonic acid is the main product formed.
At high temperature about 373 K, p-phenol sulphonic acid is the main product formed.
o-phenol sulphonic acid: IUPAC name is 2-Hydroxy benzene sulphonic acid
p-phenol sulphonic acid : IUPAC name is 4-Hydroxy benzene sulphonic acid
Phenols are aromatic hydroxy compounds. In phenols, one or more hydroxyl group is directly attached to the aromatic (benzene) nucleus.
Phenols are also classified as monohydric, dihydric and trihydric or polyhydric as their molecules contain one, two, three or more OH groups.
Examples of Phenols
Monohydric
Phenol
2-Bromophenol
m-Cresol
p-Cresol
Dihydric
1,2-Dihydroxy benzene
Trihydric
1,2,3-Trihydroxy benzene
If OH group is not directly attached to be carbon atom in the benzene ring, but present in the molecule as a part of the alkyl side chain group, then the compound is not termed as phenol.
It is called aromatic alcohol because it resembles aliphatic alcohols in its characteristics.
Examples:
benzyl alcohol or Phenylmethanol
2-Phenylethanol
Nomenclature of Phenols
Common system
IUPAC system
All substituted phenols are named as derivatives of phenol.
The position of the substituents w.r.t.-OH group is indicated by Arabic numerals(with the carbon carrying-OH group being numbered 1).
Examples
2-Methyl phenol - Methyl group CH3 is present adjacent to OH group in phenol.
3-Methyl phenol - Methyl group CH3 is present in third position when OH group position is counted as 1 in phenol.
2-Bromophenol - Bromine is present adjacent to OH group in phenol.
--------------------
Phenols: Methods of Preparation
1. Alkali fusion of sodium benzene sulphonate
NaOH is fused with sodium benzene sulphonate at 573 - 623 K, sodium phenoxide is formed. This on acidification gives phenol.
2. From diazonium salts
An acqueous solution of benzene diazonium salt on warming gives phenol
3. By decarboxylation of sodium salt of salicyclic acid
Fusion of sodium salicylate with soda lime (NaOH and CaO mixture).
sodium phenoxide is formed. This on acidification gives phenol.
4. From Grignard reagent
when oxygen gas is bubbled through an ethereal solution of phenyl magnesium bromide (Grignard reagent RMgX), if forms an oxy compound which upon hydrolysis with dilute mineral acid gives phenol.
Commercial Preparation of Phenols
1. From chlorobenzene (Dow's Process)
Chlorobenzene is heated with 10% acqueous sodium hydroxide solution at about 623 K under 200 atmospheres andin the presence of copper salt acting as catalyst to form sodium phenoxide. The sodium salt when treated with dilute HCl, gives phenol.
2. From cumene
Air or oxygen is passed through a suspension of cumene in acqueous sodium carbonate solution in presence of cobalt or manganese naphthenate catalyst. The oxidation product is cumene hydroperoxide.
The hydroperoxide is then decomposed by hot dilute sulphuric acid when phenol is formed withliberation of acetone. Acetone is removed from phenol by distillation.
3. From Benzene (Raschig's method)
Vapours of HCl are passed over benzene at 500 K in the presence of copper chloride and excess of air to form chlorobenzene. Steam is then passed through chlorobenzene at 800 K in the presence of silica as catalyst to give phenol.
4. Phenol prepared using benzene and H2SO4
Benzene is heated with excess of concentrated sulphuric acid at about 388 K to give benzene sulphonic acid.
It is neutralized with sodium hydroxide solution, when sodium benzene sulphonate is obtained.
Dry sodium benzene sulphonate is next fused with excess of caustic soda at about 573 K when it yields sodium phenate (or sodium phenoxide).
Sodium phenate is decomposed by dilute sulphuric acid to give phenol.
Physical properties
1. State and smell: Phenols are colourless crystalline solids or liquids. They have characteristic phenolic odours.
2. solubility: Phenols are sparingly soluble in water
3. Boiling points: Higher than the boiling points of the aromatic hydrocarbons of comparable molecular masses.
BP of phenol (mol. mass = 94) is 455 K while that of toluene (mol mass = 92) is 384 K. This higher BP is due to intermolecular hydrogen bonding in phenols.
Chemical properties
Can be classified into three groups
A. Reactions of phenolic group (_OH group)
B. Reactions of benzene ring
C. Special reactions
A. Reactions of phenolic group (_OH group)
1. Action with zinc dust
2. Action with ammonia
3. Action with acid chlorides and acid anhydrides
4. Action with benzyl chloride
B. Reactions of benzene ring
1. Bromination
Action of Bromine water on phenol: When phenol is treated with bromine water, it gets decolourised giving a white precipitate of 2,4,6, tribromophenol.
Action of Bromine in CS-2 on phenol:o-Bromophenol + p-Bromophenol mixture is obtained. p-Bromophenol is the major product.
2. Nitration
Action of dilute nitirc acid on phenol: a mixture of o-nitrophenol and p-nitrophenol is formed.
Action of conc. nitric acid in the presence of conc. sulphuric acid on phenol: 2,4,6-trinitrophenol is formed. This is picric acid.
3. Nitrosation
The reaction which involves the substitution by nitroso grou (-NO) is called nitrosation.
Phenol reacts with nitrous acid (NaNO2 + HCl) at low temperature (280 K) to form p-nitrosophenol. It can be further oxidized with dil HNO3 to give p-nitrophenol.
4. Sulphonation: Covered as a special topic
5. Alkylation
Special reactions of Phenol
1. Kolbe's reaction: special topic
2. Reimer-Tiemann reaction: special topic
3. coupling reaction
4. Reaction with pthalic anhydride
5. Condensation with formaldehyde
6. Hydrogenation
7. Oxidation
8. Reaction with ferric chloride
9. Libermann's test
Acidity of Phenols
Phenols are weakly acidic in nature (Ka = 10^-10).
They turn blue litmus read and react with alkali metals and alkalies to form their salts.
The acidic character of phenol is due to polar OH bond.
Phenol is weaker acid than carboxylic acid.
Like carboxylic, it also does not react with sodium carbonate and sodium bicarbonate.
Phenols are more acidic than alcohols.
Phenol is a resonance hybrid of 5 structures. Three of the structures develop +charge on oxygen and facilitate release of H+.
Phenoxide ion which results when H+ is released from phenol is also a resonance hybrid but it is more stable than phenol. Hence the reaction is in favour of phenoxide ion. Therefore phenol is acidic and more acidic than alcohols.
Halogenation of Phenols (electrophylic substitution reaction)
The reaction does not require a lewis acid catalyst. Benzene requires a lewis acid catalyst for halogenation.
Bromine in CS2 reacts with phenol to give 4-Bromophenol(?)
Chlorine at high temperatures react with phenol to give 4-chlorophenol(?)
See http://clem.mscd.edu/~wiederm/oc2chp/oc2chpphenols/page3.htm
You can download a chapter on phenols from
http://www.diacritech.com/samples/science_and_medical/chemistry.pdf
Phenols are readily brominated in an aqueous solution forming 2, 4, 6-tribromophenol. This is a white precipitate.
Mostly p-bromophenol is obtained along with ortho bromophenol by treatment
of phenol with bromine in CCl4 or CS2.
Treatment of phenols with aqueous solutions of bromine results in replacement
of every hydrogen ortho or para to the -OH group. Bromination may
even cause displacement of certain other groups to yield tribromophenol.
Nitration of phenols
Action of dilute nitirc acid on phenol: a mixture of o-nitrophenol and p-nitrophenol is formed.
Action of conc. nitric acid in the presence of conc. sulphuric acid on phenol: 2,4,6-trinitrophenol is formed. This is picric acid.
Sulphonation
Action of conc. sulphuric acid at different temperatures on phenol:
Pheno reacts with conc. sulphuric acid to form a mixture of o-, and p-phenol sulphonic acid.
At low temperature about 288 to 293 K, o-phenol sulphonic acid is the main product formed.
At high temperature about 373 K, p-phenol sulphonic acid is the main product formed.
o-phenol sulphonic acid: IUPAC name is 2-Hydroxy benzene sulphonic acid
p-phenol sulphonic acid : IUPAC name is 4-Hydroxy benzene sulphonic acid
AIEEE Chemistry Unit 23C Ethers
Ethers
(a) An ether is an oxygen bridge between two organic compounds.
For example: R-O-R'
(b) An alcohol is a special case of an ether, one in which one R is replaced with a hydrogen (for that matter, water could very well be considered to be an ether in which both R groups are replaced with hydrogens, though in this latter case one would no longer be referring to a organic compound).
(c) Conversely, the hydrogen of a hydroxyl group may be replaced with a organic compound. It occurs when two alcohols join through the loss of a water molecule in a reaction called dehydration synthesis: R-OH + HO-R' --> R-O-R' + HOH
(a) An ether is an oxygen bridge between two organic compounds.
For example: R-O-R'
(b) An alcohol is a special case of an ether, one in which one R is replaced with a hydrogen (for that matter, water could very well be considered to be an ether in which both R groups are replaced with hydrogens, though in this latter case one would no longer be referring to a organic compound).
(c) Conversely, the hydrogen of a hydroxyl group may be replaced with a organic compound. It occurs when two alcohols join through the loss of a water molecule in a reaction called dehydration synthesis: R-OH + HO-R' --> R-O-R' + HOH
AIEEE Chemistry Unit 23D Aldehydes and Ketones
Aldehydes contain carbonyl group C=O as functional group and the carbonyl atom carries at least one H atom.
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Nomenclature of Aldehydes and Ketones
Common names are used for the simplest aldehydes and ketones:
formaldehyde, butyraldehyde, benzaldehyde,
acetone, benzophenone, acetophenone
Common names are also used for carbonyl-containing substituent groups,
which are known collectively as acyl groups:
formyl, acetyl, benzoyl
Traditional names are used for a great many aldehydes and ketones which
were recognized as substances long before systems of nomenclature were
developed:
cinnamaldehyde, furfural, acrolein
Structure of Aldehydes and Ketones
• The carbonyl carbon of an aldehyde or ketone is sp2-hybridized.
-• The bond angle is close to 120° (trigonal planar).
• The carbon-oxygen double bond consists of:
– A sigma C-O bond
– A pi C=O bond
Properties of Aldehydes and Ketones
Aldehydes and ketones are polar molecules because the C=O bond has a
dipole moment:
• Their polarity makes aldehydes and ketones have higher boiling points than
alkenes of similar molecular weight.
• Aldehydes and ketones are not hydrogen bond donors (they can can’t donate a
proton); therefore, they have lower boiling points than alcohols of similar
molecular weight.
• Aldehydes and ketones are hydrogen bond acceptors; this makes them have
considerable solubilities in water.
Ketones such as acetone are good solvents because they dissolve both aqueous and organic compounds
Acetone is a polar, aprotic solvent.
Reactions of Aldehydes and Ketones
The reactions of aldehydes and ketones can be divided into two main
categories:
– Reactions of the carbonyl group
- Reactions involving the alpha-carbon
Carbonyl group reactions fall into three main groups:
– Reactions with acids
– Addition reactions
– Oxidation
Reactions with acids:
– The carbonyl oxygen is weakly basic.
– Both Bronsted and Lewis acids can interact with a lone pair of electrons on
the carbonyl oxygen.
Addition Reactions
– Carbonyl groups in aldehydes and ketones undergo addition reactions.
– This is one of the most important reactions of the carbonyl group.
Addition reactions occur by two different mechanisms:
– Base-catalyzed addition (under basic or neutral conditions)
– Acid-catalyzed addition (under acidic conditions)
• In some cases, we can carry out the same overall reaction using either set of
conditions (acidic or basic).
Oxidation
Carbonyl groups in aldehydes and ketones may be oxidized to form
compounds at the next “oxidation level”, that of carboxylic acids.
• Alcohols are oxidized to aldehydes and ketones
(example: biological oxidation of ethanol to acetaldehyde)
• The carbonyl group may be further oxidized to carboxylic acids
Basicity of Aldehydes and Ketones
Reactions which occur at the carbonyl oxygen xygen of aldehydes and ketones:
– The weakly basic carbonyl oxygen reacts with protons or Lewis acids
– The protonated form of the aldehyde or ketone is resonance-stabilized
– This gives the aldehyde/ketone conjugate acid carbocation character
Protonated aldehydes and ketones can be thought of as alpha-hydroxy carbocations
• When an alkyl group replaces (conceptually) the proton, an alpha-alkoxy
carbocation is formed:
Addition Using Grignard Reagents
• Primary, secondary and tertiary alcohols may be formed in the reactions of
aldehydes or ketones with Grignard reagents.
primary alcohols from formaldehyde
secondary alcohols from aldehydes
tertiary alcohols from ketones
Gatterman reaction?
The Gattermann reaction, named for the German chemist Ludwig Gattermann, in organic chemistry refers to a reaction of hydrocyanic acid with an aromatic compound, in this case benzene, under catalysis of with Friedel-Crafts catalyst (aluminium chloride).The reaction is similar to the Friedel-Crafts reaction.
See: http://en.wikipedia.org/wiki/Gattermann_reaction
Reducing R-COCl to an aldehyde?
By catalytic hydrogenation in the presence of palladium (Pd) catalyst supported over barium sulphate The catalytic mixture is poisoned by the addition of a small amount of sulphur or quinoline. This reaction is known as Rosemmund reduction.
Getting an aldehyde from methylbenzene
by oxidation
Getting ketone from alcohols?
By oxidation of secondary alcohols
-----------------
Ketones
In ketones, also carbonyl group C=O is the functional group. But the carbonyl carbon does not contain any H atoms, but it is attached to two alkyl or aryl groups.
Nomenclature of Aldehydes and Ketones
Common names are used for the simplest aldehydes and ketones:
formaldehyde, butyraldehyde, benzaldehyde,
acetone, benzophenone, acetophenone
Common names are also used for carbonyl-containing substituent groups,
which are known collectively as acyl groups:
formyl, acetyl, benzoyl
Traditional names are used for a great many aldehydes and ketones which
were recognized as substances long before systems of nomenclature were
developed:
cinnamaldehyde, furfural, acrolein
Structure of Aldehydes and Ketones
• The carbonyl carbon of an aldehyde or ketone is sp2-hybridized.
-• The bond angle is close to 120° (trigonal planar).
• The carbon-oxygen double bond consists of:
– A sigma C-O bond
– A pi C=O bond
Properties of Aldehydes and Ketones
Aldehydes and ketones are polar molecules because the C=O bond has a
dipole moment:
• Their polarity makes aldehydes and ketones have higher boiling points than
alkenes of similar molecular weight.
• Aldehydes and ketones are not hydrogen bond donors (they can can’t donate a
proton); therefore, they have lower boiling points than alcohols of similar
molecular weight.
• Aldehydes and ketones are hydrogen bond acceptors; this makes them have
considerable solubilities in water.
Ketones such as acetone are good solvents because they dissolve both aqueous and organic compounds
Acetone is a polar, aprotic solvent.
Reactions of Aldehydes and Ketones
The reactions of aldehydes and ketones can be divided into two main
categories:
– Reactions of the carbonyl group
- Reactions involving the alpha-carbon
Carbonyl group reactions fall into three main groups:
– Reactions with acids
– Addition reactions
– Oxidation
Reactions with acids:
– The carbonyl oxygen is weakly basic.
– Both Bronsted and Lewis acids can interact with a lone pair of electrons on
the carbonyl oxygen.
Addition Reactions
– Carbonyl groups in aldehydes and ketones undergo addition reactions.
– This is one of the most important reactions of the carbonyl group.
Addition reactions occur by two different mechanisms:
– Base-catalyzed addition (under basic or neutral conditions)
– Acid-catalyzed addition (under acidic conditions)
• In some cases, we can carry out the same overall reaction using either set of
conditions (acidic or basic).
Oxidation
Carbonyl groups in aldehydes and ketones may be oxidized to form
compounds at the next “oxidation level”, that of carboxylic acids.
• Alcohols are oxidized to aldehydes and ketones
(example: biological oxidation of ethanol to acetaldehyde)
• The carbonyl group may be further oxidized to carboxylic acids
Basicity of Aldehydes and Ketones
Reactions which occur at the carbonyl oxygen xygen of aldehydes and ketones:
– The weakly basic carbonyl oxygen reacts with protons or Lewis acids
– The protonated form of the aldehyde or ketone is resonance-stabilized
– This gives the aldehyde/ketone conjugate acid carbocation character
Protonated aldehydes and ketones can be thought of as alpha-hydroxy carbocations
• When an alkyl group replaces (conceptually) the proton, an alpha-alkoxy
carbocation is formed:
Addition Using Grignard Reagents
• Primary, secondary and tertiary alcohols may be formed in the reactions of
aldehydes or ketones with Grignard reagents.
primary alcohols from formaldehyde
secondary alcohols from aldehydes
tertiary alcohols from ketones
Gatterman reaction?
The Gattermann reaction, named for the German chemist Ludwig Gattermann, in organic chemistry refers to a reaction of hydrocyanic acid with an aromatic compound, in this case benzene, under catalysis of with Friedel-Crafts catalyst (aluminium chloride).The reaction is similar to the Friedel-Crafts reaction.
See: http://en.wikipedia.org/wiki/Gattermann_reaction
Reducing R-COCl to an aldehyde?
By catalytic hydrogenation in the presence of palladium (Pd) catalyst supported over barium sulphate The catalytic mixture is poisoned by the addition of a small amount of sulphur or quinoline. This reaction is known as Rosemmund reduction.
Getting an aldehyde from methylbenzene
by oxidation
Getting ketone from alcohols?
By oxidation of secondary alcohols
-----------------
AIEEE Chemistry Unit 23E Carboxylic Acids
Carboxylic acids are the compound containing carboxyl group in their molecules.
-c with a double bond with oxygen and single bond with OH
The carboxyl group is made up of carbonyl C with double bond with oxygen, and hydroxyl group OH. The carboxyl is formed carbo + oxyl.
These acides can be aliphatic or aromatic.
aliphatic acids
Formic acid HCOOH
Acetic acid CH-3COOH
Isobutyric acid (Branched)
aromatic acids
Bezoic acid : H in benzene substituted by COOH
m-Nitrobenzoic acid: One more H substituted by NO-2
o-Toluic acid (o refers to ortho) Benzoic acid with one more H substituted by CH-3
Dicarboxyic acids
Oxalic acid
Malonic acid
Succinic acid
Phthalic acid - It is an aromatic carboxylic acid
In the nomenclature, in common system, position of the sustituents is indicated by the greek letter alpha, beta, gamma and delta.
the carbon atom adjacent ot the carboxyl carbon is assigned the letter α, thenext carbon on chain is beta an so on.
According to the IUPAC system, the name of the acid is derived from the corresponding alkane by replacing the terminal 'e' with the '-oic' and adding the word acid.
The position of the substituents is indicated by the following rules:
1. The longest chain containing the carboxylic group (-COOH) is selected.
2. The carbon chain is numbered form the carboxylic acid group. The carbon of carboxyl group is always given number one.
3. The position of the substituents is indicated by the number.
Methods of Preparation of Monocarboxylic Acids:
1. From oxidation of primary alcohols
2. By oxidation of aldehydes and ketones.
3. By Hydrolysis of cyanides (or Nitriles)
4. By Grignard reaction
5. By hydrolysis of esters
6. By carboxylation of alkenes
7. From trihalogen derivatives of hydrocarbons
8. Aromatic acids from alkyl benzenes
Physical properties
State
B.P.
M.P.
Solubility
Reactions of carboxylic Acids
covered under the following heads
A. reactions due to hydrogen atom of carboxyl group
B. reactions due to OH carboxyl group
C. reactions due to carboxyl group
D. reactions due to alkyl group and benzene ring.
A. Reactions due to hydrogen atom of carboxyl group
1. Acidic Properties
B. Reactions due to OH carboxyl group
1. Formation of an acid anhydride
2. Formation of Esters
3. Formation of amides
4. Formation of acid chlorides
C. Reactions due to carboxyl group
1. Decarboxylation
2. Reduction
3. Action of bromine on silver salt of the acid
D. reactions due to alkyl group and benzene ring.
1. Halogenation
2. Ring substitution in aromatic acids
-c with a double bond with oxygen and single bond with OH
The carboxyl group is made up of carbonyl C with double bond with oxygen, and hydroxyl group OH. The carboxyl is formed carbo + oxyl.
These acides can be aliphatic or aromatic.
aliphatic acids
Formic acid HCOOH
Acetic acid CH-3COOH
Isobutyric acid (Branched)
aromatic acids
Bezoic acid : H in benzene substituted by COOH
m-Nitrobenzoic acid: One more H substituted by NO-2
o-Toluic acid (o refers to ortho) Benzoic acid with one more H substituted by CH-3
Dicarboxyic acids
Oxalic acid
Malonic acid
Succinic acid
Phthalic acid - It is an aromatic carboxylic acid
In the nomenclature, in common system, position of the sustituents is indicated by the greek letter alpha, beta, gamma and delta.
the carbon atom adjacent ot the carboxyl carbon is assigned the letter α, thenext carbon on chain is beta an so on.
According to the IUPAC system, the name of the acid is derived from the corresponding alkane by replacing the terminal 'e' with the '-oic' and adding the word acid.
The position of the substituents is indicated by the following rules:
1. The longest chain containing the carboxylic group (-COOH) is selected.
2. The carbon chain is numbered form the carboxylic acid group. The carbon of carboxyl group is always given number one.
3. The position of the substituents is indicated by the number.
Methods of Preparation of Monocarboxylic Acids:
1. From oxidation of primary alcohols
2. By oxidation of aldehydes and ketones.
3. By Hydrolysis of cyanides (or Nitriles)
4. By Grignard reaction
5. By hydrolysis of esters
6. By carboxylation of alkenes
7. From trihalogen derivatives of hydrocarbons
8. Aromatic acids from alkyl benzenes
Physical properties
State
B.P.
M.P.
Solubility
Reactions of carboxylic Acids
covered under the following heads
A. reactions due to hydrogen atom of carboxyl group
B. reactions due to OH carboxyl group
C. reactions due to carboxyl group
D. reactions due to alkyl group and benzene ring.
A. Reactions due to hydrogen atom of carboxyl group
1. Acidic Properties
B. Reactions due to OH carboxyl group
1. Formation of an acid anhydride
2. Formation of Esters
3. Formation of amides
4. Formation of acid chlorides
C. Reactions due to carboxyl group
1. Decarboxylation
2. Reduction
3. Action of bromine on silver salt of the acid
D. reactions due to alkyl group and benzene ring.
1. Halogenation
2. Ring substitution in aromatic acids
AIEEE Chemistry ORGANIC COMPOUNDS CONTAINING OXYGEN
General methods of preparation, properties, reactions and uses.
ALCOHOLS, PHENOLS AND ETHERS:
Alcohols: Identification of primary, secondary and tertiary alcohols; mechanism of dehydration.
Phenols: Acidic nature, electrophilic substitution reactions: halogenation, nitration and sulphonation, Reimer - Tiemann reaction.
Ethers: Structure.
Aldehyde and Ketones: Nature of carbonyl group;
Nucleophilic addition to >C=O group, relative reactivities of aldehydes and ketones; Important reactions such as - Nucleophilic addition reactions (addition of HCN, NH3 and its derivatives), Grignard reagent; oxidation; reduction (Wolff Kishner and Clemmensen); acidity of ? - hydrogen, aldol condensation, Cannizzaro reaction, Haloform reaction; Chemical tests to distinguish between aldehydes and Ketones.
Carboxylic Acids: Acidic strength and factors affecting it.
----------------
Alcohols - Introduction
The hydroxy derivatives of aliphatic hydrocarbons are termed alcohols. They contain one or more hydroxyl (OH) groups.
Example:
Methyl Alcohol CH-3OH
Ehtyl alcohol C-2H-5OH also written as CH-3CH-2OH
Propyl alcohol C-3H-7OH also writtenas CH-3CH-2CH-2OH
They are classified according to the number of hydroxyl groups in the molecule.
One OH group in the molecule Monohydric alcohol
Two OH groups in the molecule Dihydric alcohol HOCH-2CH-2OH
Three OH groups in the molecule Trihydric alcohol
More than one OH group cannot be present on the same carbon atom. In such as a case, the compound will be extremely unstable and it will change into aldehyde. (This will be another topic in the syllabus itself)
Monohydric alcohols are further classified into Primary (1°), secondary(2°) and tertiary (3°) alcohols
Primary alcohols have one or none alkyl groups on the carbon bonded to -OH group.
secondary alcohols have two alkyl groups on the carbon bonded to -OH group.
Tertiary alcohols have three alkyl groups on the carbon bonded to -OH group.
IUPAC Nomenclature of Alcohols
Methanol
Ethanol
Propan-1-ol
Propan-2-ol
Butan-2-ol
2-Methylpropan-2-ol
Methods of Preparation of Alcohols
General Methods
1. preparation from haloalkanes
2. By reduction of aldehydes, ketones and esters
3. From Grignard reagents (RMgX)
4. By hydrolysis of eters
5. From alkenes
----a). hydration of alkenes
----b). Hydroboration oxidation reduction
----c). Oxymercuration - reduction
6. From aliphatic primary amines
Industrial Methods
1. Hydration of alkenes
2. Oxo Process
3. Fermentation of carbohydrates
4. manufacture of methanol
Physical Properties of alcohols
1. Physical state
2. solubility
3. Boiling points
4. Intoxicating effects
Chemical properties of alcohols
The reactions of alcohols are decribed under the following classification
A. Reactions involving cleavage of oxygen-hydrogen bond.
B. Reactions involving cleavage of carbon - oxygen bond
C. Reactions involving cleavage of both the alkyl and hydroxyl groups
A. Reactions involving cleavage of oxygen-hydrogen bond.
1. Reaction with active metals - acidic character
2. Reaction with metal hydrides
3. Reaction with carboxylic acids (esterification)
4. Reaction with grignard reagents.
5. Reaction with acyl chloride or acid anhydride
B. Reactions involving cleavage of carbon - oxygen bond
1. Reaction with hydrogen halides
2. Reaction with phosphorus halides
3. Reaction with thionyl chloride
C. Reactions involving cleavage of both the alkyl and hydroxyl groups
1. Acidic dehydration
2. Oxidation
3. dehydrogenation
Esterification
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
The function of concentrated sulphuric acid is to act as protonating agent as well as a dehydrating agent.
RCOOH + HOR' ↔ RCOOR' + H2O with H2SO4 as catalyst
CH3COOH + HOC2H5 ↔ CH3COOC2H5 + H2O with H2SO4 as catalyst
The reaction is reversible is nature. Double headed arrow is used to indicate it. The equilibrium can be shifted toward the forward direction by removing water as soon as it is formed.
If dry HCL gas is used as a catalyst, the reaction is called Fisher=Speier esterification.
It is is difficult to prepare esters of tertiary alcohols becasue bulky groups in the alcohol decrease rate of reaction or esterification. This is termed as stearic hindrance of bulky groups.
As noted above in the reactions, esterification involved the cleavage of the O-H bonds of the alcohol. This was proved by using alcohol with isotopic O18 which can be tracked using isotopic tracer technique. It was found that this oxygen is present in the resulting ester which means that the oxygen in the alcohol is going into the ester and hydrogen is going into the water molecules.
Dehydration
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
Dehydration of alcohols to ethers or alkenes can also be brought about by passing the vapour of the alcohols over heated alumina catalyst under different conditions
Oxidation
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkalineor acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
Different classes of alcohols differ from each other in their ease of oxidation and also give different products.
(i) Primary alcohols: Primary alcohols are easily oxidized. First an aldehyde is formed and then from it carboxylic acid is formed. Both the aldehyde and the resulting acid contain the same number of carbon atoms as the starting alcohol.
(ii) Secondary alcohols: Ease of oxidation is still there. But they are oxidized to ketone and under strong conditions they are further oxidized to form a mixture of acids. While the ketone contains the same number of carbon atoms as the starting alcohol, the acids formed contain lesser number of carbon atoms.
(iii) It is difficult to oxidize tertiarly alcohols.
When treated with acidic oxidizing agents under very strong conditions they form first ketones and then acids.
Both the ketones and acids contain lesser number of carbon atoms than the starting alcohols.
Reaction with sodium
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas an form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to gibve Sodium ethoxide and hydrogen
This reaction shows that alcohols are acidic in nature.
The acidic nature is due to the presence of polar O-H bond.
Alcohols are weak acids even weaker than water.
Reaction with phosphorus halides
Phosphorus halides such as PCl5, Pcl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
Haloalkanes : Chloroethane, Bromoethane, Iodoethane
Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
Alcohols get converted into alkylhalides. As alkyl halides are insoluble in water, their presence is indicated by the appearance of turbidity in the reaction mixture.
The time required for the formation of alkyl halides and appearance of turbidity is very less in the tertiary alcohols.
in the case of secondary alcohols, it takes five minutes.
A primary alcohol produces turbidity only after heating.
Thus alcohols can be distinguished using Lucas test.
Conversion of alcohols into aldehydes and ketones
This topic was already covered in the topic of oxidation.
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
ALCOHOLS, PHENOLS AND ETHERS:
Alcohols: Identification of primary, secondary and tertiary alcohols; mechanism of dehydration.
Phenols: Acidic nature, electrophilic substitution reactions: halogenation, nitration and sulphonation, Reimer - Tiemann reaction.
Ethers: Structure.
Aldehyde and Ketones: Nature of carbonyl group;
Nucleophilic addition to >C=O group, relative reactivities of aldehydes and ketones; Important reactions such as - Nucleophilic addition reactions (addition of HCN, NH3 and its derivatives), Grignard reagent; oxidation; reduction (Wolff Kishner and Clemmensen); acidity of ? - hydrogen, aldol condensation, Cannizzaro reaction, Haloform reaction; Chemical tests to distinguish between aldehydes and Ketones.
Carboxylic Acids: Acidic strength and factors affecting it.
----------------
Alcohols - Introduction
The hydroxy derivatives of aliphatic hydrocarbons are termed alcohols. They contain one or more hydroxyl (OH) groups.
Example:
Methyl Alcohol CH-3OH
Ehtyl alcohol C-2H-5OH also written as CH-3CH-2OH
Propyl alcohol C-3H-7OH also writtenas CH-3CH-2CH-2OH
They are classified according to the number of hydroxyl groups in the molecule.
One OH group in the molecule Monohydric alcohol
Two OH groups in the molecule Dihydric alcohol HOCH-2CH-2OH
Three OH groups in the molecule Trihydric alcohol
More than one OH group cannot be present on the same carbon atom. In such as a case, the compound will be extremely unstable and it will change into aldehyde. (This will be another topic in the syllabus itself)
Monohydric alcohols are further classified into Primary (1°), secondary(2°) and tertiary (3°) alcohols
Primary alcohols have one or none alkyl groups on the carbon bonded to -OH group.
secondary alcohols have two alkyl groups on the carbon bonded to -OH group.
Tertiary alcohols have three alkyl groups on the carbon bonded to -OH group.
IUPAC Nomenclature of Alcohols
Methanol
Ethanol
Propan-1-ol
Propan-2-ol
Butan-2-ol
2-Methylpropan-2-ol
Methods of Preparation of Alcohols
General Methods
1. preparation from haloalkanes
2. By reduction of aldehydes, ketones and esters
3. From Grignard reagents (RMgX)
4. By hydrolysis of eters
5. From alkenes
----a). hydration of alkenes
----b). Hydroboration oxidation reduction
----c). Oxymercuration - reduction
6. From aliphatic primary amines
Industrial Methods
1. Hydration of alkenes
2. Oxo Process
3. Fermentation of carbohydrates
4. manufacture of methanol
Physical Properties of alcohols
1. Physical state
2. solubility
3. Boiling points
4. Intoxicating effects
Chemical properties of alcohols
The reactions of alcohols are decribed under the following classification
A. Reactions involving cleavage of oxygen-hydrogen bond.
B. Reactions involving cleavage of carbon - oxygen bond
C. Reactions involving cleavage of both the alkyl and hydroxyl groups
A. Reactions involving cleavage of oxygen-hydrogen bond.
1. Reaction with active metals - acidic character
2. Reaction with metal hydrides
3. Reaction with carboxylic acids (esterification)
4. Reaction with grignard reagents.
5. Reaction with acyl chloride or acid anhydride
B. Reactions involving cleavage of carbon - oxygen bond
1. Reaction with hydrogen halides
2. Reaction with phosphorus halides
3. Reaction with thionyl chloride
C. Reactions involving cleavage of both the alkyl and hydroxyl groups
1. Acidic dehydration
2. Oxidation
3. dehydrogenation
Esterification
Alcohols react with monocarboxylic acids, in the presence of concentrated sulphuric acid or dry HCL gas as catalyst, to from esters. This reaction is known as esterification.
The function of concentrated sulphuric acid is to act as protonating agent as well as a dehydrating agent.
RCOOH + HOR' ↔ RCOOR' + H2O with H2SO4 as catalyst
CH3COOH + HOC2H5 ↔ CH3COOC2H5 + H2O with H2SO4 as catalyst
The reaction is reversible is nature. Double headed arrow is used to indicate it. The equilibrium can be shifted toward the forward direction by removing water as soon as it is formed.
If dry HCL gas is used as a catalyst, the reaction is called Fisher=Speier esterification.
It is is difficult to prepare esters of tertiary alcohols becasue bulky groups in the alcohol decrease rate of reaction or esterification. This is termed as stearic hindrance of bulky groups.
As noted above in the reactions, esterification involved the cleavage of the O-H bonds of the alcohol. This was proved by using alcohol with isotopic O18 which can be tracked using isotopic tracer technique. It was found that this oxygen is present in the resulting ester which means that the oxygen in the alcohol is going into the ester and hydrogen is going into the water molecules.
Dehydration
When alcohols are heated with conc. or H3PO4, at 443 K, they get dehydrated to form alkenes.
The ease of dehydration of alcohol follows the order 3>2>1 which is also the order of stability of carbocation.
Dehydration of alcohols to ethers or alkenes can also be brought about by passing the vapour of the alcohols over heated alumina catalyst under different conditions
Oxidation
The oxidation of alcohols can be carried out by a number of reagents such as acqueous, alkalineor acidified KMnO4, acidified Na2Cr2O7, nitric acid, chromic acid, etc.
Different classes of alcohols differ from each other in their ease of oxidation and also give different products.
(i) Primary alcohols: Primary alcohols are easily oxidized. First an aldehyde is formed and then from it carboxylic acid is formed. Both the aldehyde and the resulting acid contain the same number of carbon atoms as the starting alcohol.
(ii) Secondary alcohols: Ease of oxidation is still there. But they are oxidized to ketone and under strong conditions they are further oxidized to form a mixture of acids. While the ketone contains the same number of carbon atoms as the starting alcohol, the acids formed contain lesser number of carbon atoms.
(iii) It is difficult to oxidize tertiarly alcohols.
When treated with acidic oxidizing agents under very strong conditions they form first ketones and then acids.
Both the ketones and acids contain lesser number of carbon atoms than the starting alcohols.
Reaction with sodium
The cleavage in this reaction will be in the OH bond. Alcohols react with active metals to liberate hydrogen gas an form metal alkoxide.
Ethanol or Ethyl alcohol reacts with sodium to gibve Sodium ethoxide and hydrogen
This reaction shows that alcohols are acidic in nature.
The acidic nature is due to the presence of polar O-H bond.
Alcohols are weak acids even weaker than water.
Reaction with phosphorus halides
Phosphorus halides such as PCl5, Pcl3, PBr3 and PI3 react with alcohols to form corresponding haloalkanes.
Haloalkanes : Chloroethane, Bromoethane, Iodoethane
Reaction with ZnCl2/conc.-HCl
This is a reaction or test to distinguish various categories of alcohols and is termed Lucas test.
In this test, an alcohol is treated with an equimolar mixture of concentrated hydrochloric acid and anhydrous ZnCl2 (called Lucas reagent).
Alcohols get converted into alkylhalides. As alkyl halides are insoluble in water, their presence is indicated by the appearance of turbidity in the reaction mixture.
The time required for the formation of alkyl halides and appearance of turbidity is very less in the tertiary alcohols.
in the case of secondary alcohols, it takes five minutes.
A primary alcohol produces turbidity only after heating.
Thus alcohols can be distinguished using Lucas test.
Conversion of alcohols into aldehydes and ketones
This topic was already covered in the topic of oxidation.
Oxidation of primary alcohol gives aldehydes.
Oxidation of secondary alcohols gives ketones.
It is difficult to oxidize tertiary alcohols.
AIEEE Chemistry UNIT 24 Organic Compounds Containing Nitrogen
General methods of preparation, properties, reactions and uses.
Amines: Nomenclature, classification, structure, basic character and identification of primary, secondary and tertiary amines and their basic character.
Diazonium Salts: Importance in synthetic organic chemistry.
-----------------
Amines are regarded as derivatives of ammonia in which one, two or all three hydrogen atoms are replaced by alkyl or aryl group.
NH3 - H = RNH2; (Primary amine) characteritic group NH2 amino
RNH2 - H = R2NH;(secondary amine) characteritic group NH imino
R2NH - H = R3N (tertiary amine) characteritic group N tert-nitrogen
The amines are classified as primary, secondary and tertiary according to one, two or three hydrogen atoms of ammonia are replaced by alkyl or aryl groups.
In addition, there is another class known as quaternary ammonium compounds. These compounds are regarded as derivatives of ammonium salts in which all the four hydrogen atoms are replaced by alkyl or aryl groups.
Nomenclature of amines
IUPAC NAMES
Aliphatic amines
Methanamine
Ethanamine
1-Propanamine
2-Propanamines
N-methylmethanamine
N-Methylethanamine
N,N-Dimethylmethanamine
Aromatic amines
Benzenamine - can also be written as amino benzene
2-Methylbenzenamine
3-Methylbenzenamine
4-Methylbenzenamine
N-Methylbenzenamine
N,N-Dieethylbenzenamine
Preparation of amines
1. From alkyl halides
2. From Nitro compounds
3.From nitriles (cyanides) and isonitriles (isocyanides)
4. From amides
5. From oximes
6. from aldehydes and ketones
Industrial preparation
1. from alcohols
2.from aniline
Physical properties
1. State and smell
2. B.P.
Chemical Properties
1. Reaction with water (Basic character of amines)
2. Reaction with acids
3. Reaction with metal ions
4. Alkylation
5. Acylation (reaction with acid chlorides and acid anhydrides)
6. Benzoylation
7. schiff's base formation
8. Oxidation
9. Carbalamine reaction
10. Reaction with nitrous acid
11. Reaction with Grignard reagent
12. Carbon disulphide
13. Carbonyl chloride
14. Ring substitution in aromatic amines
15. coupling of diazonium salts
Amines: Nomenclature, classification, structure, basic character and identification of primary, secondary and tertiary amines and their basic character.
Diazonium Salts: Importance in synthetic organic chemistry.
-----------------
Amines are regarded as derivatives of ammonia in which one, two or all three hydrogen atoms are replaced by alkyl or aryl group.
NH3 - H = RNH2; (Primary amine) characteritic group NH2 amino
RNH2 - H = R2NH;(secondary amine) characteritic group NH imino
R2NH - H = R3N (tertiary amine) characteritic group N tert-nitrogen
The amines are classified as primary, secondary and tertiary according to one, two or three hydrogen atoms of ammonia are replaced by alkyl or aryl groups.
In addition, there is another class known as quaternary ammonium compounds. These compounds are regarded as derivatives of ammonium salts in which all the four hydrogen atoms are replaced by alkyl or aryl groups.
Nomenclature of amines
IUPAC NAMES
Aliphatic amines
Methanamine
Ethanamine
1-Propanamine
2-Propanamines
N-methylmethanamine
N-Methylethanamine
N,N-Dimethylmethanamine
Aromatic amines
Benzenamine - can also be written as amino benzene
2-Methylbenzenamine
3-Methylbenzenamine
4-Methylbenzenamine
N-Methylbenzenamine
N,N-Dieethylbenzenamine
Preparation of amines
1. From alkyl halides
2. From Nitro compounds
3.From nitriles (cyanides) and isonitriles (isocyanides)
4. From amides
5. From oximes
6. from aldehydes and ketones
Industrial preparation
1. from alcohols
2.from aniline
Physical properties
1. State and smell
2. B.P.
Chemical Properties
1. Reaction with water (Basic character of amines)
2. Reaction with acids
3. Reaction with metal ions
4. Alkylation
5. Acylation (reaction with acid chlorides and acid anhydrides)
6. Benzoylation
7. schiff's base formation
8. Oxidation
9. Carbalamine reaction
10. Reaction with nitrous acid
11. Reaction with Grignard reagent
12. Carbon disulphide
13. Carbonyl chloride
14. Ring substitution in aromatic amines
15. coupling of diazonium salts
Subscribe to:
Posts (Atom)
