JEE Main & Advanced Chemistry Aldehydes, Ketones Some Commercially Important Aliphatic Carbonyl Compounds

Some Commercially Important Aliphatic Carbonyl Compounds

Category : JEE Main & Advanced

Formaldehyde : Formaldehyde is the first member of the aldehyde series. It is present in green leaves of plants where its presence is supposed to be due to the reaction of \[C{{O}_{2}}\] with water in presence of sunlight and chlorophyll.

 

(1) Preparation

 

(i) \[2C{{H}_{3}}OH+{{O}_{2}}\underset{300-400{}^\circ C}{\mathop{\xrightarrow{\text{Platinised asbestos}}}}\,\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\]

 

\[C{{H}_{3}}OH+[O]\underset{{{H}_{2}}S{{O}_{4}}}{\mathop{\xrightarrow{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}}}\,\ HCHO+{{H}_{2}}O\]

 

(ii) \[C{{H}_{3}}OH\underset{300-400{}^\circ C}{\mathop{\xrightarrow{Cu\ \text{ or }Ag}}}\,\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\]

 

(iii) \[\underset{\text{Calcium}\ \text{formate}}{\mathop{Ca{{(HCOO)}_{2}}}}\,\xrightarrow{\text{Heat}}\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\]

 

(iv) \[C{{H}_{2}}=C{{H}_{2}}+{{O}_{3}}\]\[\underset{Pd}{\mathop{\xrightarrow{{{H}_{2}}}}}\,\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\]

 

(v) \[\underset{\text{Methane}}{\mathop{C{{H}_{4}}}}\,+{{O}_{2}}\underset{Catalyst}{\mathop{\xrightarrow{\text{Mo-oxide}}}}\,\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\]

 

(vi) \[CO+{{H}_{2}}\xrightarrow{\text{Elec}\text{. discharge}}\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\]

 

(2) Physical properties

 

(i) It is a colourless, pungent smelling gas.

 

(ii) It is extremely soluble in water. Its solubility in water may be due to hydrogen bonding between water molecules and its hydrate.

 

(iii) It can easily be condensed into liquid. The liquid formaldehyde boils at \[-{{21}^{o}}C\].

 

(iv) It causes irritation to skin, eyes, nose and throat.

 

(v) Its solution acts as antiseptic and disinfectant.

 

(3) Uses

 

(i) The 40% solution of formaldehyde (formalin) is used as disinfectant, germicide and antiseptic. It is used for the preservation of biological specimens.

 

(ii) It is used in the preparation of hexamethylene tetramine (urotropine) which is used as an antiseptic and germicide.

 

(iii) It is used in silvering of mirror.

 

(iv) It is employed in manufacture of synthetic dyes such as para-rosaniline, indigo, etc.

 

(v) It is used in the manufacture of formamint (by mixing formaldehyde with lactose) – a throat lozenges.

 

(vi) It is used for making synthetic plastics like bakelite, urea-formaldehyde resin, etc.

 

(vii) Rongalite – a product obtained by reducing formaldehyde sodium bisulphite derivative with zinc dust and ammonia and is used as a reducing agent in vat dyeing.

 

Acetaldehyde

 

Acetaldehyde is the second member of the aldehyde series. It occurs in certain fruits. It was first prepared by Scheele in 1774 by oxidation of ethyl alcohol.

 

(1) Preparation : It may be prepared by any of the general methods. The summary of the methods is given below

 

(i) By oxidation of ethyl alcohol with acidified potassium dichromate or with air in presence of a catalyst like silver at \[{{300}^{o}}C\].

 

(ii) By dehydrogenation of ethyl alcohol. The vapours of ethyl alcohol are passed over copper at \[{{300}^{o}}C\].

 

(iii) By heating the mixture of calcium acetate and calcium formate.

 

(iv) By heating ethylidene chloride with caustic soda or caustic potash solution.

 

(v) By the reduction of acetyl chloride with hydrogen in presence of a catalyst palladium suspended in barium sulphate (Rosenmund's reaction).

 

(vi) By the reduction of \[C{{H}_{3}}CN\] with stannous chloride and HCl in ether and hydrolysis (Stephen's method).

 

(vii) By hydration of acetylene with dil. \[{{H}_{2}}S{{O}_{4}}\] and \[HgS{{O}_{4}}\] at \[{{60}^{o}}C\].

 

(viii) By ozonolysis of butene-2 and subsequent breaking of ozonide.

 

(ix) Laboratory preparation : Acetaldehyde is prepared in the laboratory by oxidation of ethyl alcohol with acidified potassium dichromate or acidified sodium dichromate.

 

\[{{K}_{2}}C{{r}_{2}}{{O}_{7}}+4{{H}_{2}}S{{O}_{4}}\xrightarrow{{}}{{K}_{2}}S{{O}_{4}}+C{{r}_{2}}{{(S{{O}_{4}})}_{3}}+4{{H}_{2}}O+3[O]\]

 

\[[C{{H}_{3}}C{{H}_{2}}OH+O\xrightarrow{{}}C{{H}_{3}}CHO+{{H}_{2}}O]\times 3\]

\[\underset{\begin{smallmatrix}\text{Potassium} \\\text{dichromate}\end{smallmatrix}}{\mathop{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}}\,+\underset{\text{Ethyl}\,\text{alcohol}}{\mathop{3C{{H}_{3}}C{{H}_{2}}OH}}\,+\underset{\text{Sulphuric acid}}{\mathop{4{{H}_{2}}S{{O}_{4}}}}\,\xrightarrow{{}}\]   \[\underset{\begin{smallmatrix}\text{Potassium}\\\text{sulphate}\end{smallmatrix}}{\mathop{{{K}_{2}}S{{O}_{4}}}}\,+\underset{\begin{smallmatrix}\text{Chromic}\\\text{sulphate}\end{smallmatrix}}{\mathop{C{{r}_{2}}{{(S{{O}_{4}})}_{3}}}}\,+\underset{\text{Acetaldehyde}}{\mathop{3C{{H}_{3}}CHO}}\,+\underset{\text{Water}}{\mathop{7{{H}_{2}}O}}\,\]

 

To recover acetaldehyde, the distillate is treated with dry ammonia when crystallised product, acetaldehyde ammonia, is formed. It is filtered and washed with dry ether. The dried crystals are then distilled with dilute sulphuric acid when pure acetaldehyde is collected.

 

\[C{{H}_{3}}CHO+N{{H}_{3}}\to \,\underset{\text{Acetaldehyde ammonia}}{\mathop{\overset{OH}{\mathop{C{{H}_{3}}\overset{|\ \ \ \ }{\mathop{-CH-}}\,N{{H}_{2}}}}\,}}\,\xrightarrow{{{H}_{2}}S{{O}_{4}}}\]  \[\underset{\text{Acetaldehyde}}{\mathop{C{{H}_{3}}CHO}}\,\ +{{(N{{H}_{4}})}_{2}}S{{O}_{4}}\]

 

(x) Manufacture : Acetaldehyde can be manufactured by one of the following methods:

 

(a) By air oxidation of ethyl alcohol

 

\[2C{{H}_{3}}C{{H}_{2}}OH+{{O}_{2}}\underset{300{}^\circ C}{\mathop{\xrightarrow{Ag}}}\,2C{{H}_{3}}CHO+2{{H}_{2}}O\]

 

(b) By dehydrogenation of alcohol

 

\[C{{H}_{3}}C{{H}_{2}}OH\underset{300{}^\circ C}{\mathop{\xrightarrow{Cu}}}\,C{{H}_{3}}CHO\]

 

(c) By hydration of acetylene

 

\[CH\equiv CH+{{H}_{2}}O\underset{{{H}_{2}}S{{O}_{4}}(40%)}{\mathop{\xrightarrow{HgS{{O}_{4}},(1%),60{}^\circ C}}}\,C{{H}_{3}}CHO\]

 

(d) From ethylene (Wacker process)

 

\[{{H}_{2}}C=C{{H}_{2}}+{{O}_{2}}\underset{{{H}_{2}}O}{\mathop{\xrightarrow{PdC{{l}_{2}},CuC{{l}_{2}}}}}\,{{H}_{3}}C-CHO\]

 

(2) Physical properties

(i) Acetaldehyde is a colourless volatile liquid. It boils at \[{{21}^{o}}C\].

(ii) It has a characteristic pungent smell.

(iii) It is soluble in water, chloroform, ethyl alcohol and ether. Its aqueous solution has a pleasant odour. In water, it is hydrated to a considerable extent to form ethylidene diol.

 

\[C{{H}_{3}}CHO+{{H}_{2}}O\xrightarrow{{}}C{{H}_{3}}CH{{(OH)}_{2}}\]

 

(3) Uses : Acetaldehyde is used :

 

(i) In the preparation of acetic acid, acetic anhydride, ethyl acetate, chloral, 1,3-butadiene (used in rubbers), dyes and drugs.

 

(ii) As an antiseptic inhalent in nose troubles.

 

(iii) In the preparation of paraldehyde (hypnotic and sporofic) and metaldehyde (solid fuel).

 

(iv) In the preparation of acetaldehyde ammonia (a rubber accelerator).

 

Comparative Study Of Formaldehyde And Acetaldehyde

S.No. Reaction Formaldehyde HCHO Acetaldehyde \[\mathbf{C}{{\mathbf{H}}_{\mathbf{3}}}\mathbf{CHO}\]
Similarities
1.

Addition of hydrogen

(a) \[{{H}_{2}}\] in presence of  catalyst, Ni, Pd or Pt

(b) \[LiAl{{H}_{4}}\] (ether)

(c) Amalgamated zinc + conc. HCl (Clemmenson reduction)

Forms methyl alcohol

\[HCHO+{{H}_{2}}\xrightarrow{{}}C{{H}_{3}}OH\]

Forms methyl alcohol

Forms methane

\[HCHO+4H\xrightarrow{{}}C{{H}_{4}}+{{H}_{2}}O\]

Forms ethyl alcohol

\[C{{H}_{3}}CHO+{{H}_{2}}\xrightarrow{{}}C{{H}_{3}}C{{H}_{2}}OH\]

Forms ethyl alcohol

Forms ethane

\[C{{H}_{3}}CHO+4H\xrightarrow{{}}{{C}_{2}}{{H}_{6}}+{{H}_{2}}O\]
2. Addition of \[NaHS{{O}_{3}}\] solution

Forms bisulphite addition product

\[HCHO+NaHS{{O}_{3}}\xrightarrow{{}}C{{H}_{2}}(OH)S{{O}_{3}}Na\]

Forms bisulphite addition product

\[C{{H}_{3}}CHO+NaHS{{O}_{3}}\xrightarrow{{}}\]

                         \[C{{H}_{3}}CH(OH)S{{O}_{3}}Na\]
3. Addition of HCN Forms formaldehyde cyanohydrin \[HCHO+HCN\xrightarrow{{}}C{{H}_{2}}(OH)CN\] Forms acetaldehyde cyanohydrin \[C{{H}_{3}}CHO+HCN\xrightarrow{{}}\]                                  \[C{{H}_{3}}CH(OH)CN\]
4. Addition of Grignard reagent followed by hydrolysis

Forms ethyl alcohol

\[\underset{-Mg(OH)I}{\mathop{\xrightarrow{{{H}_{2}}O}}}\,C{{H}_{3}}C{{H}_{2}}OH\]

Forms isopropyl alcohol

\[C{{H}_{3}}CHO+C{{H}_{3}}MgI\xrightarrow{{}}\]                 \[\underset{\,\,\,\,C{{H}_{3}}}{\mathop{C{{H}_{3}}\underset{\,\,\,|}{\mathop{-C}}\,HOMgI}}\,\underset{-Mg(OH)I}{\mathop{\xrightarrow{{{H}_{2}}O}}}\,\]                                 \[\underset{\,\,\,C{{H}_{3}}}{\mathop{C{{H}_{3}}\underset{|\ \ \ \ }{\mathop{-CH-}}\,OH}}\,\]

5.

With hydroxylamine

\[N{{H}_{2}}OH\]

Forms formaldoxime

\[C{{H}_{2}}=O+{{H}_{2}}NOH\xrightarrow{-{{H}_{2}}O}\]                                             \[C{{H}_{2}}=NOH\]

Forms acetaldoxime

\[C{{H}_{3}}CH=O+{{H}_{2}}NOH\xrightarrow{-{{H}_{2}}O}\]                                \[C{{H}_{3}}CH=NOH\]

6.

With hydrazine

\[(N{{H}_{2}}N{{H}_{2}})\]

Forms formaldehyde hydrazone

\[C{{H}_{2}}O+{{H}_{2}}N\ N{{H}_{2}}\xrightarrow{-{{H}_{2}}O}\]                                           \[C{{H}_{2}}=NN{{H}_{2}}\]  

Forms acetaldehyde hydrazone

\[C{{H}_{3}}CH=O+{{H}_{2}}NN{{H}_{2}}\xrightarrow{-{{H}_{2}}O}\]                              \[C{{H}_{3}}CH=NN{{H}_{2}}\]

7.

With phenyl hydrazine

\[({{C}_{6}}{{H}_{5}}NHN{{H}_{2}})\]

Forms formaldehyde phenyl hydrazone

\[C{{H}_{2}}=O+{{H}_{2}}NNH{{C}_{6}}{{H}_{5}}\xrightarrow{-{{H}_{2}}O}\]                                    \[C{{H}_{2}}=NNH{{C}_{6}}{{H}_{5}}\]

Forms acetaldehyde phenyl hydrazone

\[C{{H}_{3}}CH=O+{{H}_{2}}NNH{{C}_{6}}{{H}_{5}}\] \[\xrightarrow{-{{H}_{2}}O}C{{H}_{3}}CH=NNH{{C}_{6}}{{H}_{5}}\]

8.

With semicarbazide

\[({{H}_{2}}NNHCON{{H}_{2}})\]

Forms formaldehyde semicarbazone

\[C{{H}_{2}}=O+{{H}_{2}}NNHCON{{H}_{2}}\xrightarrow{-{{H}_{2}}O}\]                                 \[C{{H}_{2}}=NNHCON{{H}_{2}}\]

Forms acetaldehyde semicarbazone

\[C{{H}_{3}}CH=O+{{H}_{2}}NNHCON{{H}_{2}}\] \[\xrightarrow{-{{H}_{2}}O}C{{H}_{3}}CH=NNHCON{{H}_{2}}\]

9.

With alcohol

\[({{C}_{2}}{{H}_{5}}OH)\] in presence of acid

Forms ethylal

\[{{H}_{2}}C=O+2{{C}_{2}}{{H}_{5}}OH\xrightarrow{HCl}\]                                        

Forms acetaldehyde diethyl acetal

\[C{{H}_{3}}CHO+2{{C}_{2}}{{H}_{5}}OH\xrightarrow{HCl}\]

10.

With thioalcohols

\[({{C}_{2}}{{H}_{5}}SH)\]in presence of acid

Forms thio ethylal

\[{{H}_{2}}C=O+2{{C}_{2}}{{H}_{5}}SH\xrightarrow{{}}\]                                        

Forms acetaldehyde diethyl thioacetal

\[C{{H}_{3}}CH=O+2{{C}_{2}}{{H}_{5}}SH\xrightarrow{{}}\]

11.

Oxidation with acidified

\[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]

Forms formic acid

\[HCHO+O\xrightarrow{{}}HCOOH\]

Forms acetic acid

\[C{{H}_{3}}CHO+O\xrightarrow{{}}C{{H}_{3}}COOH\]

12. With Schiff's reagent Restores pink colour of Schiff's reagent Restores pink colour of Schiff's reagent
13. With Tollen's reagent

Gives black precipitate of  Ag or silver mirror

\[A{{g}_{2}}O+HCHO\xrightarrow{{}}2Ag+HCOOH\]

Gives black precipitate of Ag or silver mirror

\[A{{g}_{2}}O+C{{H}_{3}}CHO\xrightarrow{{}}\]                                            \[2Ag+C{{H}_{3}}COOH\]

14. With Fehling's solution or Benedict's solution

Gives red precipitate of cuprous oxide

\[2CuO+HCHO\xrightarrow{{}}C{{u}_{2}}O+HCOOH\]

Gives red precipitate of cuprous oxide

\[2CuO+C{{H}_{3}}CHO\xrightarrow{{}}\]                           \[C{{u}_{2}}O+C{{H}_{3}}COOH\]

15. Polymerisation

Undergoes polymerisation

                                             

Undergoes polymerisation

Dissimilarities
16.

With 

\[PC{{l}_{5}}\]

No reaction

Forms ethylidene chloride

                                   

\[+POC{{l}_{3}}\]

17. With chlorine No reaction

Forms chloral

\[C{{H}_{3}}CHO+3C{{l}_{2}}\xrightarrow{{}}CC{{l}_{3}}CHO\]                                               \[+3HCl\]

18.

With 

\[Se{{O}_{2}}\]

No reaction

Forms glyoxal

\[C{{H}_{3}}CHO+Se{{O}_{2}}\xrightarrow{{}}CHO.CHO\]                                        \[+Se+{{H}_{2}}O\]

19.

Iodoform reaction

 \[({{I}_{2}}+NaOH)\]

No reaction

Forms iodoform

\[C{{H}_{3}}CHO+3{{I}_{2}}+4NaOH\xrightarrow{{}}\] \[CH{{l}_{3}}+HCOONa+3NaI+3{{H}_{2}}O\]

20. With dil. alkali (Aldol condensation) No reaction

Forms aldol

\[C{{H}_{3}}CHO+HC{{H}_{2}}CHO\xrightarrow{{}}\]                     \[C{{H}_{3}}CH(OH)C{{H}_{2}}CHO\]

21. With conc. NaOH (Cannizzaro's reaction)

Forms sodium formate and methyl alcohol

\[2HCHO+NaOH\xrightarrow{{}}HCOONa\]\[+C{{H}_{3}}OH\]

Forms a brown resinous mass
22. With ammonia

Forms hexamethylene tetramine (urotropine)

\[6HCHO+4N{{H}_{3}}\xrightarrow{{}}{{(C{{H}_{2}})}_{6}}{{N}_{4}}+6{{H}_{2}}O\]

Forms addition product, acetaldehyde ammonia

\[C{{H}_{3}}CHO+N{{H}_{3}}\xrightarrow{{}}\]

23. With phenol Forms bakelite plastic No reaction
24. With urea Forms urea-formaldehyde plastic No reaction
25.

Condensation in presence of

\[Ca{{(OH)}_{2}}\]

Form formose (a mixuture of sugars) No reaction
           

Inter conversion of formaldehyde and acetaldehyde

 

(1) Ascent of series : Conversion of formaldehyde into acetaldehyde

 

(i) \[\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\xrightarrow{{{H}_{2}}/Ni}\underset{\begin{smallmatrix} \text{Methyl} \\ \text{alcohol} \end{smallmatrix}}{\mathop{C{{H}_{3}}OH}}\,\xrightarrow{PC{{l}_{5}}}\underset{\begin{smallmatrix} \text{Methyl} \\ \text{chloride} \end{smallmatrix}}{\mathop{C{{H}_{3}}Cl}}\,\underset{KCN}{\mathop{\xrightarrow{\text{Alc}\text{.}}}}\,\]

 

\[\underset{\begin{smallmatrix} \text{Methyl} \\ \text{cyanide} \end{smallmatrix}}{\mathop{C{{H}_{3}}CN}}\,\xrightarrow{Na/\text{Alcohol}}\underset{\text{Ethyl amine}}{\mathop{C{{H}_{3}}C{{H}_{2}}N{{H}_{2}}}}\,\underset{HCl}{\mathop{\xrightarrow{NaN{{O}_{2}}}}}\,\]

 

\[\underset{\text{Ethyl alcohol}}{\mathop{C{{H}_{3}}C{{H}_{2}}OH}}\,\underset{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}{\mathop{\xrightarrow{{{H}_{2}}S{{O}_{4}}\text{(dil}\text{.)}}}}\,\underset{\text{Acetaldehyde}}{\mathop{C{{H}_{3}}CHO}}\,\]

 

(ii) \[\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\underset{\text{Ether}}{\mathop{\xrightarrow{C{{H}_{3}}MgI}}}\,C{{H}_{3}}C{{H}_{2}}OMgI\xrightarrow{{{H}_{3}}{{O}^{+}}}\]

 

\[\underset{\text{Ethyl alcohol}}{\mathop{C{{H}_{3}}C{{H}_{2}}OH}}\,\underset{300{}^\circ C}{\mathop{\xrightarrow{Cu}}}\,\underset{\text{Acetaldehyde}}{\mathop{C{{H}_{3}}CHO}}\,\]

 

(iii) \[\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\underset{{{H}_{2}}S{{O}_{4}}}{\mathop{\xrightarrow{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}}}\,\underset{\text{Formic acid}}{\mathop{HCOOH}}\,\xrightarrow{Ca{{(OH)}_{2}}}\]

 

\[\underset{\text{Calcium formate}}{\mathop{{{(HCOO)}_{2}}Ca}}\,\underset{\text{heat}}{\mathop{\xrightarrow{{{(C{{H}_{3}}COO)}_{2}}Ca}}}\,\underset{\text{Acetaldehyde}}{\mathop{C{{H}_{3}}CHO}}\,\]

 

(2) Descent of series : Conversion of acetaldehyde into formaldehyde

 

(i) \[\underset{\text{Acetaldehyde}}{\mathop{C{{H}_{3}}CHO}}\,\underset{{{H}_{2}}S{{O}_{4}}}{\mathop{\xrightarrow{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}}}\,\underset{\text{Acetic acid}}{\mathop{C{{H}_{3}}COOH}}\,\xrightarrow{N{{H}_{3}}}\]

 

\[\underset{\text{Amm}\text{. acetate}}{\mathop{C{{H}_{3}}COON{{H}_{4}}}}\,\xrightarrow{\text{Heat}}\underset{\text{Acetamide}}{\mathop{C{{H}_{3}}CON{{H}_{2}}}}\,\xrightarrow{B{{r}_{2}}/KOH}\]

 

\[\underset{\text{Methyl amine}}{\mathop{C{{H}_{3}}N{{H}_{2}}}}\,\underset{HCl}{\mathop{\xrightarrow{NaN{{O}_{2}}}}}\,C{{H}_{3}}OH\underset{300{}^\circ C}{\mathop{\xrightarrow{Cu}}}\,\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\]

 

(ii) \[\underset{\text{Acetaldehyde}}{\mathop{C{{H}_{3}}CHO}}\,\underset{{{H}_{2}}S{{O}_{4}}}{\mathop{\xrightarrow{{{K}_{2}}C{{r}_{2}}{{O}_{7}}}}}\,\underset{\text{Acetic acid}}{\mathop{C{{H}_{3}}COOH}}\,\xrightarrow{NaOH}\underset{\text{Sod}\text{.acetate}}{\mathop{C{{H}_{3}}COONa}}\,\]

 

\[\underset{\text{heat}}{\mathop{\xrightarrow{\text{Sodalime}}}}\,\underset{\text{Methane}}{\mathop{C{{H}_{4}}}}\,\underset{hv}{\mathop{\xrightarrow{C{{l}_{2}}}}}\,C{{H}_{3}}Cl\xrightarrow{AgOH}\]

 

 \[C{{H}_{3}}OH\underset{300{}^\circ C}{\mathop{\xrightarrow{Cu}}}\,\underset{\text{Formaldehyde}}{\mathop{HCHO}}\,\]       

 

Acetone

It is a symmetrical (simple) ketone and is the first member of the homologous series of ketones. In traces, it is present in blood and urine.

(1) Preparation :

 

 

(vii) From pyroligneous acid : Pyroligneous acid containing acetic acid, acetone and methyl alcohol is distilled in copper vessel and the vapours are passed through hot milk of lime. Acetic acid combines to form nonvolatile calcium acetate. The unabsorbed vapours of methanol and acetone are condensed and fractionally distilled. Acetone distills at \[{{56}^{o}}C\].

 

The acetone thus obtained is purified with the help of sodium bisulphite.

 

(2)   Physical properties : (i) It is a colourless liquid with characteristic pleasant odour.

 

(ii)   It is inflammable liquid. It boils at \[{{56}^{o}}C\].

 

(iii) It is highly miscible with water, alcohol and ether.

 

(3)   Chemical properties

 

 

 

If acetone would be in excess in ketal condensation or catalyst \[(ZnC{{l}_{2}}/\text{dry}\,HCl)\] is used then three moles of acetone undergoes condensation polymerisation and form a compound called ‘Phorone’.

 

 

Molecular mass of phorone = 3 mole of acetone – 2 mole of \[{{H}_{2}}O\]     

 

Reformatsky reaction: This reaction involves the treatment of aldehyde and ketone with a bromo acid ester in presence of metallic zinc to form \[\beta -\]hydroxy ester, which can be easily dehydrated into \[\alpha ,\,\,\beta -\]unsaturated ester.

 

(a)\[BrC{{H}_{2}}COO{{C}_{2}}{{H}_{5}}+Zn\xrightarrow{\text{Benzene}}\underset{\text{Organo zinc compound}}{\mathop{Br-\overset{\oplus }{\mathop{Zn}}\,-C{{H}_{2}}COO{{C}_{2}}{{H}_{5}}}}\,\]

 

(b) Addition to carbonyl group

 

 

\[\underset{\left[ Zn\,\,\,\,\begin{matrix} Br\ \,  \\ OH  \\ \end{matrix} \right]}{\mathop{\xrightarrow{HOH/{{H}^{+}}}}}\,\underset{\beta \text{-hydroxyesters}}{\mathop{C{{H}_{3}}-\underset{OH\,\,\,}{\overset{C{{H}_{3}}\,}{\mathop{\underset{|}{\overset{|}{\mathop{{{C}_{{}}}}}}\,\,\,\,-\,\,}}}\,\underset{COO{{C}_{2}}{{H}_{5}}}{\mathop{\underset{|\,\,\,\,\,\,\,\,\,}{\mathop{C{{H}_{2}}}}\,\,\,\,\,\,\,\,\,\,\,\,\,}}\,}}\,\]

 

\[\xrightarrow{{}}C{{H}_{3}}-\overset{C{{H}_{3}}}{\mathop{\overset{|\,\,\,\,\,\,\,\,}{\mathop{C\,\,=\,}}\,}}\,CH-COO{{C}_{2}}{{H}_{5}}\]

 

(4) Uses

 

(i) As a solvent for cellulose acetate, cellulose nitrate, celluloid, lacquers, resins, etc.

 

(ii)   For storing acetylene.

 

(iii) In the manufacture of cordite – a smoke less powder explosive.

 

(iv)   In the preparation of chloroform, iodoform, sulphonal and chloretone.

 

(v)    As a nailpolish remover.

 

(vi)           In the preparation of an artificial scent (ionone), plexiglass (unbreakable glass) and synthetic rubber.

 

(5)   Tests

 

(i) Legal's test : When a few drops of freshly prepared sodium nitroprusside and sodium hydroxide solution are added to an aqueous solution of acetone, a wine colour is obtained which changes to yellow on standing.

 

(ii)   Indigo test : A small amount of orthonitrobenzaldehyde is added to about  2 ml. of acetone and it is diluted with KOH solution and stirred. A blue colour of indigotin is produced.

 

(iii)  Iodoform test : Acetone gives iodoform test with iodine and sodium hydroxide or iodine and ammonium hydroxide.

 

 Comparison Between Acetaldehyde And Acetone

 

Reaction Acetaldehyde Acetone
Similarities    

1. Reduction with

\[{{H}_{2}}\] and Ni or \[LiAl{{H}_{4}}\]                                 

Forms ethyl alcohol

\[C{{H}_{3}}CHO+{{H}_{2}}\xrightarrow{Ni}C{{H}_{3}}C{{H}_{2}}OH\]

Forms isopropyl alcohol

\[C{{H}_{3}}COC{{H}_{3}}+{{H}_{2}}\xrightarrow{{}}C{{H}_{3}}CHOHC{{H}_{3}}\]

2. Clemmensen's reduction

(Zn/Hg and conc. HCl)

Forms ethane (an alkane)

\[C{{H}_{3}}CHO+4H\xrightarrow{{}}C{{H}_{3}}C{{H}_{3}}+{{H}_{2}}O\]

Forms propane (an alkane)

\[C{{H}_{3}}COC{{H}_{3}}+4H\xrightarrow{{}}C{{H}_{3}}C{{H}_{2}}C{{H}_{3}}+{{H}_{2}}O\]
3. Addition of HCN Forms acetaldehyde cyanohydrin

Forms acetone cyanohydrin

4. Addition of \[NaHS{{O}_{3}}\]

White crystalline derivative

White crystalline derivative

5. Grignard reagent followed by hydrolysis Forms isopropyl alcohol \[C{{H}_{3}}CHO+C{{H}_{3}}MgI\xrightarrow{{}}{{(C{{H}_{3}})}_{2}}CH-OMgI\]\[\xrightarrow{{{H}_{2}}O}C{{H}_{3}}CHOHC{{H}_{3}}\] Forms tertiary butyl alcohol \[{{(C{{H}_{3}})}_{2}}CO+C{{H}_{3}}MgI\xrightarrow{{}}{{(C{{H}_{3}})}_{3}}COMgI\] \[\xrightarrow{{{H}_{2}}O}\,{{(C{{H}_{3}})}_{3}}COH\]
6. With hydroxylamine         \[(N{{H}_{2}}OH)\] Forms acetaldoxime  (an oxime) \[C{{H}_{3}}CHO+{{H}_{2}}NOH\xrightarrow{{}}C{{H}_{3}}CH=NOH\] Forms acetoxime (an oxime) \[{{(C{{H}_{3}})}_{2}}CO+{{H}_{2}}NOH\,\,\,\xrightarrow{{}}\,{{(C{{H}_{3}})}_{2}}C=NOH\]
7. With hydrazine \[(N{{H}_{2}}N{{H}_{2}})\] Forms acetaldehyde hydrazone \[C{{H}_{3}}CHO+{{H}_{2}}NN{{H}_{2}}\xrightarrow{{}}C{{H}_{3}}CH=NN{{H}_{2}}\] Forms acetone hydrazone \[{{(C{{H}_{3}})}_{2}}CO+{{H}_{2}}NN{{H}_{2}}\xrightarrow{{}}\,{{(C{{H}_{3}})}_{2}}C=NN{{H}_{2}}\]
8. With phenyl hydrazine \[({{C}_{6}}{{H}_{5}}NHN{{H}_{2}})\] Forms acetaldehyde phenylhydrazone \[C{{H}_{3}}CHO+{{H}_{2}}NNH{{C}_{6}}{{H}_{5}}\xrightarrow{{}}\] \[C{{H}_{3}}CH=NNH{{C}_{6}}{{H}_{5}}\] Forms acetone phenyl hydrazone \[{{(C{{H}_{3}})}_{2}}CO+{{H}_{2}}NNH{{C}_{6}}{{H}_{5}}\xrightarrow{{}}\] \[{{(C{{H}_{3}})}_{2}}C=NNH{{C}_{6}}{{H}_{5}}\]
9. With semicarbazide \[({{H}_{2}}NNHCON{{H}_{2}})\] Forms acetaldehyde semicarbazone \[C{{H}_{3}}CHO+{{H}_{2}}NNHCON{{H}_{2}}\xrightarrow{{}}\] \[C{{H}_{3}}CH=NNHCON{{H}_{2}}\] Forms acetone semicarbazone \[{{(C{{H}_{3}})}_{2}}CO+{{H}_{2}}NNHCON{{H}_{2}}\xrightarrow{{}}\] \[{{(C{{H}_{3}})}_{2}}C=NNHCON{{H}_{2}}\]
10. With \[PC{{l}_{5}}\] Forms ethylidene chloride (Gem dihalide)

Forms isopropylidene chloride (Gem dihalide)

11. With chlorine Forms chloral (Gem trihalide) \[C{{H}_{3}}CHO+C{{l}_{2}}\xrightarrow{{}}CC{{l}_{3}}CHO\] Forms trichloro acetone (Gem trihalide) \[C{{H}_{3}}COC{{H}_{3}}+C{{l}_{2}}\xrightarrow{{}}CC{{l}_{3}}COC{{H}_{3}}\]
12. With alcohols

Forms acetal (a diether)

Forms ketal (a diether)

13. With \[Se{{O}_{2}}\]

Forms glyoxal

\[C{{H}_{3}}CHO+Se{{O}_{2}}\xrightarrow{{}}\,CHOCHO+Se+{{H}_{2}}O\]

Forms methyl glyoxal

\[{{(C{{H}_{3}})}_{2}}CO+Se{{O}_{2}}\xrightarrow{{}}C{{H}_{3}}COCHO+Se+{{H}_{2}}O\]

14.   Iodoform reaction        

\[({{I}_{2}}+NaOH)\]

Forms iodoform Forms iodoform
15. Bleaching powder Forms chloroform Forms chloroform
16. Aldol condensation with mild alkali

Forms aldol

\[2C{{H}_{3}}CHO\xrightarrow{{}}C{{H}_{3}}CHOHC{{H}_{2}}CHO\]

Forms diacetone alcohol

\[2C{{H}_{3}}COC{{H}_{3}}\xrightarrow{{}}{{(C{{H}_{3}})}_{2}}C(OH)C{{H}_{2}}COC{{H}_{3}}\]

17. Polymerisation Undergoes polymerisation Does not undergo polymerisation but gives condensation reaction

18. With

\[N{{H}_{3}}\]

Forms acetaldehyde ammonia

Forms diacetone ammonia

\[{{(C{{H}_{3}})}_{2}}CO+N{{H}_{3}}+OC{{(C{{H}_{3}})}_{2}}\xrightarrow{{}}\] \[{{(C{{H}_{3}})}_{2}}C(N{{H}_{2}})C{{H}_{2}}COC{{H}_{3}}\]

19. With conc.

\[NaOH\]

Forms brownish resinous mass No reaction

20. With

\[HN{{O}_{2}}\]

No reaction

Forms oximino acetone

\[C{{H}_{3}}COC{{H}_{3}}+HN{{O}_{2}}\xrightarrow{{}}C{{H}_{3}}COCH=NOH\]

21. With chloroform No reaction

Forms chloretone

22. With alk. sodium nitroprusside Deep red colour Red colour changes to yellow on standing
23. With sodium nitroprusside + Pyridine Blue colour No effect
24. Boiling point \[{{21}^{o}}C\] \[{{56}^{o}}C\]
Dissimilarities    
25. With Schiff's reagent Pink colour Does not give pink colour
26. With Fehling's solution Gives red precipitate No reaction
27. With Tollen's reagent Gives silver mirror No reaction

28. Oxidation with acidified

\[{{K}_{2}}C{{r}_{2}}{{O}_{7}}\]

Easily oxidised to acetic acid

\[C{{H}_{3}}CHO+O\xrightarrow{{}}C{{H}_{3}}COOH\]

Oxidation occurs with difficulty to form acetic acid

\[C{{H}_{3}}COC{{H}_{3}}+O\xrightarrow{{}}C{{H}_{3}}COOH+C{{O}_{2}}+{{H}_{2}}O\].

 



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