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Organic compounds containing C, H, O Alcohols, Phenols and Ethers

         Alcohols (R - OH), Phenols (C6H5OH), Ethers (R - O - R') are the basic compounds for the formation of detergents, antiseptics, fragrances respectively. Alkyl alcohols are classified into primary (RCH2 - OH), secondary (R2CH - OH) and tertiary (R3COH) alcohols. The order of C - O bond length in these compounds is CH3OH (142 pm) > CH3OCH3 (141 pm) > Phenol (136 pm).
 


From Grignard reagent: Aldehydes/ Ketones on reaction with RMgX followed by hydrolysis gives alcohols. In this reaction HCHO gives primary alcohol, other aldehydes give secondary alcohol, ketones give tertiary alcohols.


From CO: Methanol (wood spirit) is prepared by catalytic hydrogenation of CO at high temperature and pressure in presence of ZnO - Cr2O3 catalyst.

Methanol is used as solvent in paints, varnishes for making HCHO.


Ethyl Alochol from Molasses:
Physical Properties: As alcohols are able to form hydrogen bonds, they are soluble in water. Boiling points of alcohols are higher than hydrocarbons, ethers, haloalkanes of comparable molecular masses (due to H - bonding).
e.g.: C2H5OH (351 K) > CH3OCH3 (248 K) > C3H8 (231 K)

Chemical reactions of alcoholds:
Reactions involving cleavage of O - H bond:
Due to polar nature of O - H bond, alcohols are acidic.
Order of acid strength: RCH2OH > R2CHOH > R3COH.

Reaction with acids: The reaction between carboxylic acid with alcohol gives Ester, the reaction is called "Esterification".
     


Reactions involving cleavage of C - O bond:
Reaction with Hydrogen halides (Lucas test):
      
       A mixture of conc. HCl and ZnCl2 is called "Lucas reagent". With Lucas reagent, 3º alcohol gives turbidity immediately, 2º alcohol gives after some time, 1º alcohol do not give any turbidity.
Reaction with PCl3 & PCl5:

Dehydration:
Order of ease of dehydration: 3º alcohols > 2º alcohols > 1º alcohols


Oxidation of alcohol with CrO3 or PCC gives aldehyde, where as acidified KMnO4 gives carboxylic acid.

Copper heated upto 573 K can also be used for dehydrogenation of alcohols. In this reaction primary alcohol gives aldehyde, secondary alcohol gives ketone and tertiary alcohol gives alkene.
 

Preparation of Phenols:

Chemical properties of Phenols:

Reactions involving cleavage of O - H bond:
Acidic nature of phenols & comparision with alcohols:
        Proton (H+) donor is acid - OH is electron with drawing group and is attached to sp2 carbon of benzene ring. As electronegativity of sp2 carbon of phenol, electron density decreases on Oxygen. This will increase the polarity of O - H bond and results increase in ionisation of phenols than that of alcohols. In alkoxide ion (RO-) the negative charge is localised only on Oxygen, where as in Phenol, charge is delocalised. Due to resonance, stable phenoxide ion is formed by losing H+ ion (easily).
                        
Phenoxide ion is more stable than that of alkoxide ion acidity of phenols is more than that of alcohols. When electron with drawing groups like -NO2 are attached to benzene in ortho para positions in phenol acidic nature will increases further. From PKa data we will understand that phenol is million times more acidic than that of Ethanol.


Formation of ASPIRIN: Acetyl salicylic acid is called Aspririn. Salicylic acid on acetylation with acetic anhydride gives "ASPIRIN".


It is used as analgesic, anti inflamatory and antipyretic.


Electrophilic aromatic substitution: -OH group in phenol is ortho and para directing.


 

Kolbe's reaction: Salicylic acid is formed when phenol is treated with NaOH and CO2, H+

Reimer - Tiemann reaction: In this reaction phenol is converted into salicylaldehyde when phenol is treated with CHCl3, and aq. NaOH or aq. KOH.

ETHERS 

Compounds having R - O - R general formula called ethers.
Preparation:
By dehydration of alcohols:

      

Williamson's synthesis: Symmetrical and unsymmetrical ethers are prepared by the reaction between alkyl halide and sodium alkoxide.

SN2 attack of alkoxide ion on 1º alkyl halide takes place in this reaction.

3º alkyl halide gives alkene in this reaction (elimination reaction)


Chemical reactions:
Reactions involving cleavage of C - O bond:


 

Electrophilic substitution:


Alkylation (Friedel - Craft's):

 

ALDEHYDES, KETONES AND CARBOXYLIC ACIDS 

in preparing fabrics, flavourings, plastics, drugs, soaps, detergents, Nylon 6, 6, food preservatives, perfumes, dyes etc.


Preparation of Aldehydes & Ketones:
      If we replace one H atom in aldehyde by alkyl group, we get Ketone. Let us understand in this easiest way.
By oxidation of alcohols:

By dehydrogenation of alcohols:

By ozonolysis of alkenes:

By hydration of alkynes:


Rosenmund reduction: In this reaction, Pd - BaSO4 catalyst reduces acyl chloride into aldehyde.


Etard reaction: Methyl group is oxidised (with Cr2O2Cl2) into chromium complex, which on hydrolysis gives aldehydes
          


Gattermam - Koch reaction: When benzene is treated with CO, HCl in present of CuCl gives benzaldehyde

           


Friedel - Craft's acylation:


Chemical Reactions:
Nucleophilic addition reactions:
Addition of HCN: Aldehyde/ ketone gives cyanohydrin with HCN.


Addition of sodium hydrogen sulphite:

       
Addition of RMgX:

        
Addition of alcohols: Acetaldehyde on reaction with 1 mole of monohydric alcohol (e.g.: CH3OH) in presence of dry HCl gives hemiacetal & with 2 moles of alcohol give acetal. Ketone with ethylene glycol gives ketal.

Reduction:

Cross Aldol condensation:

Aldol condensation:

Cross Aldol condensation:


TESTS:
Tollen's Test: Tollen's reagent is ammonical silver nitrate. A bright silver mirror is formed when aldehyde is warmed with Tollen's reagent in alkaline medium.

Fehlings Test: The mixture containing equal amounts of Fehling solution A (aq. Copper sulphate) and Fehling solution B (alkaline sodium potassium tartarate) is called Fehling's reagents. When aliphatic aldehyde is heated with Fehling's solution, a reddish brown precipitate is formed.

Uses of Aldehydes & Ketones:
* They are good industrial solvents.
* 40% Formaldehyde (Formalin) is used to preserve biological specimens & to prepare the polymer bakelite.
* CH3CHO is used to prepare CH3COOH, Vinegar, polymers, drugs.
* C6H5CHO is used to perfumery & in dye industries.


CARBOXYLIC ACIDS
        The general formula of aliphatic & aromatic carboxylic acids are RCOOH & ArCOOH respectively. Aliphatic carboxylic acids with 12 to 18 carbon chain are called fatty acids.
Methods of preparation:
From primary alcohols & aldehydes:


Physical properties:
      They exists as dimer in vapour state or in aprotic solvent due to H - bonding.
Chemical Rections:
Reactions involving cleavage of O - H bond:
Acidity: They react with Na, NaOH, NaHCO3 due to acidic nature.

pKa values of strong acid is < 1, moderately strong have 1 - 5, weak acids have 5 - 15, extremely weak acids have > 15 [eg pKa of Phenol  16]


Effect of groups in decreasing acidity:
      CF3 > NO2 > CN > F > Cl > Br > I > C6H5
Reactions involving cleavage of C - OH bond:
      


Reactions involving alkyl (R) part:
Hell - Volhard - Zelinsky reaction:
 The reaction in which halogenation takes place at alpha posion of a carboxylic acid (having alpha hydrogen) when treated with a halogen (Cl2 or Br2) in presence of red Phosphorus.

       
Friedel Craft's reaction:
   


Uses of carboxylic acids:
* HCOOH is used in rubber, textile, dyeing, leather & electroplating industries.
* CH3COOH is used as solvent, as Vinegar in food industry.
* Nylon 6, 6 is prepared from HOOC ___ (CH2)4 ___ COOH.
* Sodium benzoate is used as food preservative.
* Higher fatty acids are used for the manufacture of soaps & detergents.

Posted Date : 06-08-2021

గమనిక : ప్రతిభ.ఈనాడు.నెట్‌లో కనిపించే వ్యాపార ప్రకటనలు వివిధ దేశాల్లోని వ్యాపారులు, సంస్థల నుంచి వస్తాయి. మరి కొన్ని ప్రకటనలు పాఠకుల అభిరుచి మేరకు కృత్రిమ మేధస్సు సాంకేతికత సాయంతో ప్రదర్శితమవుతుంటాయి. ఆ ప్రకటనల్లోని ఉత్పత్తులను లేదా సేవలను పాఠకులు స్వయంగా విచారించుకొని, జాగ్రత్తగా పరిశీలించి కొనుక్కోవాలి లేదా వినియోగించుకోవాలి. వాటి నాణ్యత లేదా లోపాలతో ఈనాడు యాజమాన్యానికి ఎలాంటి సంబంధం లేదు. ఈ విషయంలో ఉత్తర ప్రత్యుత్తరాలకు, ఈ-మెయిల్స్ కి, ఇంకా ఇతర రూపాల్లో సమాచార మార్పిడికి తావు లేదు. ఫిర్యాదులు స్వీకరించడం కుదరదు. పాఠకులు గమనించి, సహకరించాలని మనవి.

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