Aldehyde ketone ether

 1. The Carbonyl Group, : The functional group  is called carbonyl group. Organic compounds containing carbonyl group are aldehydes, ketones, carboxylic acids and their derivatives. The general formulae of these compounds are given below:

Derivatives of Carboxylic Acids:

The carbon atom of the carbonyl group is sp2 hybridised. The structure of carbonyl group is shown in Fig. 12.1.

The  bond is polar due to higher electronegativity of oxygen atom as compared to carbon.

2. Common and IUPAC Names of Some Aldehydes and Ketones:

Table 12.1: Common and IUPAC Names of Some Aldehydes and Ketones

Common Name	Structural Formula	IUPAC Name
Formaldehyde	HCHO	Methanal
Acetaldehyde	CH3—CHO	Ethanal
a-Methylbutyraldehyde	CH3—CH2—CαH—|CH3CHO	2-Methylbutanal
Isobutyraldehyde	CH3—CH|CH3—CHO	2-Methylpropanal
Valeraldehyde	CH3—CH2— CH2 —CH2—CHO	Pentanal
Acrolein	CH2— CH—CHO	Prop-2-enal
a-Methoxypropionaldehyde	CH3—CαH—|OCH3CHO	2-Methoxypropanal
g-Methylcyclohexane		3-Methylcyclohexanecarbaldehyde
Phthaldehyde		Benzene-1, 2-dicarbaldehyde
m-Bromobenzaldehyde		3-Bromobenzenecarbaldehyde or 3-Bromobenzaldehyde
Crotonaldehyde	CH3—CH—CH—CHO	But-2-enal
Cinnamaldehyde		3-Phenyl prop-2-enal
Acetone	CH3COCH3	Propanone
Diisopropyl ketone		2, 4-Dimethylpentan-3-one
Mesityl oxide	CH3—C==|CH3CH—COCH3	4-Methylpent-3-en-2-one
a-Methylcyclohexanone		2-Methylcyclohexanone

OHC—CH2—CH—|CHOCH2—CHOPropane−1,2,3−tricarbaldehydeCH3—C—||OCH2—C—||OCH3Pentane−2,4−dione

3. Preparation of Aldehydes

(a) By oxidation of primary alcohols

(b) By dehydrogenation of primary alcohols

R—CH2—OH1°Alcohol→573KCuR—CHOAldehyde+H2

(c) From hydrocarbons

(i) By ozonolysis of alkenes

(ii) By hydration of alkynes

CH≡≡CHAcetylene+H2O−→−−333KH2SO4/HgSO4⎡⎣⎢⎢CH2==CH|OH⎤⎦⎥⎥Unstable−→−−RearrangementCH3—CHOAcetaldehyde

(d) From acyl chloride

(e) From nitriles and esters

SnCl2+2HCl→SnCl4+2[H]

R—C≡≡N+HCl+2[H]→R—CH==NH.HCl−→−–NH4Cl+H2OR—CHOAldehyde

This reaction is called Stephen reaction

R—CN−→−−−2.H2O1.AlH(i−Bu)2R—CHOAldehyde

CH3—CH=CH—CH2—CH2—CNHex−4−enenitrile−→−−−−2.H2O1.AIH(i−Bu)2CH3—CH=CH—CH2—CH2—CHOHex−4−en−1−al

CH3—(CH2)9—C||O—O—CH2—CH3Ethylundecanoate−→−−2.H2O1.DIBAL−HCH3(CH2)9—C||O—HUndecanal

4. Preparation of Benzaldehyde

(a) By oxidation of toluene

This reaction is called Etard reaction.

(b) By side chain chlorination followed by hydrolysis

(c) By Gatterman–Koch reaction

5. Preparation of Ketones

(a) By oxidation of secondary alcohols

(b) By dehydrogenation of secondary alcohols

(c) From hydrocarbons

(i) By ozonolysis of alkenes

(ii) By hydration of alkynes

CH3—C≡≡CHPropyne−→−−−Markovnikov’sadditionH2SO4/HgSO4⎡⎣⎢⎢CH3—C==|OHCH2⎤⎦⎥⎥Unstable→CH3—C||O—CH3Acetone

(d) From acyl chlorides

2R—MgX+CdCl2→R2Cd+2MgXCl

2R′—C||O—ClAcylchloride+R2CdDialkylCadmium→2R′—C||O—RKetone+CdCl2

(e) From nitriles

6. Preparation of Aromatic Ketones

(a) By Friedel-Crafts acylation

(b) From nitriles

7. Physical Properties of Aldehydes and Ketones

(a) Physical state: Most of the aldehydes (except formaldehyde which is a gas) are liquids at room temperature. The lower ketones are colourless liquids and have a pleasant smell. The higher members are colourless solids. Aromatic ketones are usually solids with a pleasant smell.

(b) Boiling points: Aldehydes and ketones have relatively high boiling points as compared to hydrocarbons of comparable molecular masses. It is due to the reason that aldehydes and ketones contain polar carbonyl group and therefore, they have stronger dipole–dipole interactions between the opposite ends of C — O dipoles.

These dipole–dipole interactions are however, weaker than intermolecular H-bonding in alcohols. Consequently, boiling points of aldehydes and ketones are relatively lower than the alcohols of comparable molecular masses.

(c) Solubility: The lower members of aldehydes and ketones (up to four carbon atoms) are soluble in water. It is due to their capability to form hydrogen bonds with water molecules. The solubility of these compounds in water decreases with the increase in the size of alkyl group. It is because of the increase in the magnitude of non-polar part in the molecule. However, higher homologues are soluble in organic solvents.

8. Chemical Properties

Aldehydes and ketones are highly reactive compounds. Both aldehydes and ketones undergo nucleophilic addition reactions.

Explanation: The reactive nature of aldehydes and ketones is because of the presence of a polar carbonyl group. As the oxygen atom is more electronegative, therefore, it pulls the electron around itself acquiring a partial negative charge (d– ) whereas a partial positive charge (d+ ) is developed on the carbon atom.

The positively charged carbon atom of carbonyl group is then readily attacked by the nucleophilic species for initiation of the reaction. This leads to the formation of an intermediate anion which further undergoes the attack of (H+) ion or other positively charged species to form the final product. The nucleophilic reactions may be catalysed by acids or bases. The reaction in general, may be represented as:

Relative Reactivity of Aldehydes and Ketones

In general, ketones are less reactive than aldehydes on account of the following facts:

Aldehydes are generally more reactive than ketones in nucleophilic addition reactions due to steric and electronic reasons. Sterically, the presence of two relatively large substituents in ketones hinders the approach of nucleophile to carbonyl carbon than in aldehydes having only one such substituent. Electronically, aldehydes are more reactive than ketones because two alkyl groups reduce the electrophilicity of the carbonyl carbon more effectively than in former.

Some Important Nucleophilic Addition Reactions

(a) (i) Addition of hydrogen cyanide (HCN)

(ii) Addition of sodium hydrogensulphite (NaHSO3)

This reaction is useful for separation and purification of aldehydes and ketones.

(iii) Addition of Grignard reagent

(iv) Addition of alcohols

Ketones do not react with monohydric alcohols but react with dihydric alcohols to give ketals.

(b) Addition of ammonia and its derivatives

(c) Reduction

(i) Reduction to alcohols: Aldehydes and ketones are reduced to primary and secondary alcohols, respectively, by LiAlH4 or NaBH4 or H2 in the presence of Ni or Pt.

R—CHO+2[H]−→−orNaBH4LiAlH4R—CH2—OH1°Alcohol

(ii) Reduction to hydrocarbons

(Clemmensen reduction)

(Wolff–Kishner reduction)

(d) Oxidation: Aldehydes are easily oxidised to carboxylic acids on treatment with common oxidising agents or mild oxidising agent like Tollens’ reagent or Fehling’s solution.

Ketones undergo oxidation under vigorous conditions with cleavage of carbon–carbon bond.

As ketones are not oxidised by mild oxidising agents such as Tollens’ reagent and Fehling’s solution, these reagents are used to distinguish aldehydes from ketones.

Electrophilic substitution reactions:

As, —O||C—H or —O||C—R group are electron-withdrawing and, therefore they are deactivating and m-directing.

Nitration:

9. Uses of Aldehydes and Ketones

(i) A 40% aqueous solution of formaldehyde is known as formalin and is used to preserve biological specimens and to prepare bakelite.

(ii) Acetaldehydes are used as a starting material in the manufacture of acetic acid, ethyl acetate, vinyl acetate, polymers and drugs.

(iii) Benzaldehyde is used in perfumery and in dye industries.

(iv) Acetone and ethyl methyl ketone are common industrial solvents.

10. Carboxylic Acid

Organic compounds containing carboxyl group  possess sufficient acidic character and are called carboxylic acids. The carboxyl group is made up of carbonyl,  and hydroxyl, —OH group, hence, its name is carboxyl group (carb from carbonyl and oxyl from hydroxyl). Carboxylic acids may be aliphatic (R—COOH) or aromatic (Ar—COOH) depending upon whether —COOH group is attached to aliphatic alkyl chain or aryl groups, respectively.

Aliphatic monocarboxylic acids are known as fatty acids because some of their higher members (C12—C18) like palmitic acid (C15H31COOH) and stearic acid (C17H35COOH) exist in natural fats as esters of glycerol and are obtained by their hydrolysis.

Structure of Carboxyl Group

In carboxylic acids, the bonds to the carboxyl carbon lie in one plane and are separated by about 120°. The carboxylic carbon is less electrophilic than carbonyl carbon because of the possible resonance structure shown below:

11. In IUPAC system, the name of carboxylic acid is derived by replacing terminal e of the alkane with oic acid. For example,

Table 12.2: Common and IUPAC Names of Some Carboxylic Acids

Common Name	Structural Formula	IUPAC Name
Formic acid	H—C||O—O—H	Methanoic acid
Acetic acid	CH3—COOH	Ethanoic acid
Isobutyric acid	CH3—CH—|CH3COOH	2-Methyl propanoic acid
Oxalic acid	HOOC—COOH	Ethanedioic acid
Malonic acid	HOOC3—C2H2—C1OOH	Propane-1, 3-dioic acid
Succinic acid	HOOC—(CH2)2—COOH	Butane-1, 4-dioic acid
Glutaric acid	HOOC—(CH2)3—COOH	Pentane-1, 5-dioic acid
Adipic acid	HOOC—(CH2)4—COOH	Hexane-1, 6-dioic acid
Lactic acid	CH3—CH|OH—COOH	2-Hydroxy propanoic acid
Acrylic acid	CH2==CH—COOH	Prop-2-enoic acid
Crotonic acid	CH3—CH==CH—COOH	But-2-enoic acid
Benzoic acid		Benzene carboxylic acid(Benzoic acid)
Phenyl acetic acid		2-Phenylethanoic acid
Phthalic acid		Benzene-1, 2-dicarboxylic acid

CH—COOH||CH2—COOHCH2—COOHPropane−1,2,3−tricarboxylicacid

12. Methods of Preparation of Carboxylic Acids

(a) By oxidation of primary alcohols and aldehydes.

(b) From alkyl cyanides and amides.

CH3—C≡≡N−→−−H2OH+orOH–CH3—C||O—NH2Acetamide−→−−Δ–NH3H+orOH–CH3—COOHAceticacid

Acetonitrile

(c) From Grignard reagent

(d) By hydrolysis of acyl halides and acid anhydrides

(C6H5CO)2OBenzoicanhydride−→H2O2C6H5—COOHBenzoicAcid

(e) By hydrolysis of esters

Preparation of benzoic acid

(i) From alkyl benzene

(ii) From nitriles and amides

(iii) By hydrolysis of esters

(iv) From Grignard reagent

13. Physical Properties of Carboxylic Acids

(a) Physical state: The first three aliphatic acids are colourless liquids with pungent smell. The next six are oily liquids with an odour of rancid butter while the higher members are colourless, odourless, waxy solids. Benzoic acid is a crystalline solid.

(b) Solubility: Carboxylic acid molecules are polar, like alcohols, and can form intermolecular hydrogen bonds. The first four acids are miscible with water, the C5H11COOH is partly soluble and the higher acids are insoluble. It is because of the increase in the magnitude of non-polar part in the molecule. Benzoic acid is practically insoluble in water.

Carboxylic acids are soluble in less polar solvents like ether, benzene, alcohol, etc.

(c) Boiling points: Because of their ability to form intermolecular hydrogen bonding, carboxylic acids have high boiling points. The hydrogen bonds formed by the carboxylic acids are stronger than those in alcohols because O—H bond in COOH is strongly polarised due to the presence of electron-withdrawing carbonyl group in adjacent position than the O—H bond of alcohols. Therefore, the boiling points of carboxylic acids particularly lower members are higher than alcohols of comparable molecular masses.

14. Chemical Properties of Carboxylic Acids

Carboxylic acids are resonance hybrid of the following structures:

From these structures, it is clear that the carbonyl parts of the carboxyl group have a reduced double bond character. Thus, it does not give the reactions of the carbonyl group. Also it is evident that the two contributing structures of carboxylic acid are not equivalent, therefore, they are less resonance stabilized. Moreover, oxygen atom of —OH group has positive charge in structure II, this indicates its electron deficient nature. Hence, the shared pair of electrons of O—H bond will be strongly pulled towards oxygen and this makes the O—H bond quite polar. Thus, the reactions of carboxylic acids are characteristic of the carboxyl group and alkyl group.

Acidic Nature

Carboxylic acids are quite strong acids because of the presence of polar O—H group. They ionise to give hydrogen ions and hence behave as acids.

Carboxylic acids behave as fairly strong acids: This can be explained as follows:

Carboxylic acids as well as carboxylate ion both are stabilised by resonance. However, carboxylate ion is more stabilised by resonance because its contributing structures are exactly identical. On the other hand, the contributing structures of carboxylic acid involve charge separation. Since carboxylate ion is more stabilised by resonance than carboxylic acid, therefore, equilibrium lies very much in forward direction, i.e., in favour of ionised form. Hence, carboxylic acids behave as fairly strong acids.

Acidity of carboxylic acids:

Both carboxylic acid and carboxylate ion are resonance stabilised but stabilisation is far greater for the carboxylate ion than for the acid. Thus, carboxylic acids get ionised due to gain in the stability in going from carboxylic acid to the more stable carboxylate ion. Any factor that stabilises the carboxylate ion more would facilitate the release of protons and increase the acidity. Thus, electron-withdrawing substituents (Cl, NO2, CN, etc.) in a carboxylic acid would disperse the negative charge of the COO–, stabilise it and thus enhance the acid strength. On the other hand, the presence of an electron-donating substituent such as alkyl group, would intensify the negative charge on the COO– ion and thus destabilise it, making the carboxylic acid less acidic.

The effect of some substituents is as follows:

(i) Effect of electron withdrawing substituents: The electron withdrawing substituents decrease the electron density on the O—H bond thus facilitating the release of H+ ions and also stabilise the carboxylate anion by dispersal of negative charge. Thus, an electron-withdrawing group increases the strength of the acid.

(ii) Effect of electron releasing substituents—alkyl groups: The presence of electron releasing substituent intensifies the electron density in O—H bond. As a result, it adversely affects the release of H+ ions and thus decreases the acidic character.

(iii) Acidity decreases with larger alkyl groups as the +I effect of the alkyl group increases with size of alkyl group. For example, Formic acid > Acetic acid > Propanoic acid.

(iv) Acidity increases with increasing number of electron-withdrawing substituents on the a-carbon. For example, Acetic acid < Chloroacetic acid < Dichloroacetic acid (Cl2CH—COOH) < Trichloroacetic acid (Cl3C—COOH).

(v) Acidity increases with increasing electronegativity of substituents. Thus,

Iodoacetic acid (ICH2—COOH) < Bromoacetic acid (BrCH2—COOH) < Chloroacetic acid (ClCH2—COOH) < Fluoroacetic acid (FCH2—COOH).

(vi) Acidity declines with increasing distance between electron-withdrawing group and COOH group. For example, 2-Chlorobutanoic acid > 3-Chlorobutanoic acid > 4-Chlorobutanoic acid.

(vii) Unsubstituted aromatic carboxylic acids are stronger acids than unsubstituted aliphatic carboxylic acids. Benzoic acid is a stronger acid than acetic acid. Further, since formic acid does not contain any alkyl group, therefore, it is a stronger acid than benzoic acid. Thus,

Formic acid > Benzoic acid > Acetic acid

Effect of substituents on the acidic strength of benzoic acid.

(i) The electron-releasing groups such as, —CH3, —OH, —NH2, etc., tend to decrease the acid strength of benzoic acid. The electron-withdrawing groups such as —Cl, —NO2, etc., tend to increase the strength of benzoic acid.

(ii) Ortho isomer of benzoic acid is the strongest of all the isomers irrespective of the nature of the substituent. This is called ortho effect. This effect may be due to a combination of steric and electronic factors.

(iii) The acid-strengthening effect of electron-withdrawing group (e.g., —Cl, —NO2, etc.) is more pronounced at p-position than at m-position.

(iv) The acid-weakening effect of an electron-releasing substituent (e.g., —OH, —CH3, —NH2, etc.) is more pronounced at p-position than at m-position.

15. Chemical Reactions

The reaction of carboxylic acids are classified as follows:

(a) Reactions involving cleavage of O—H bond: Reaction with metals and alkalis.

2R—COOH+2Na→2R—COO–N+aSodiumcarboxylate+H2R—COOH+NaOH→R—COO–N+a+H2OR—COOH+NaHCO3→R—COO–N+a+H2O+CO2↑⏐⏐

(b) Reactions involving cleavage of C—OH bond

(i) Formation of anhydride

(ii) Esterification:

R—COOH+R′—OH−⇀↽−−−H+R—COOR′+H2O

CH3—COOHAceticacid+CH3—CH2—OH⇌H+CH3—COOCH2—CH3Ethylacetate+H2O

(iii) Reactions with PCl5, PCl3 and SOCl2

R—COOH+PCl5→RCOClAcylchloride+POCl3+HCl3R—COOH+PCl3→3RCOCl+H3PO3R—COOH+SOCl2→RCOCl+SO2+HCl

(iv) Reaction with ammonia:

R—COOH+NH3⇌R—COO–NH+→–H2OΔR—CONH2Acidamide

(c) Reaction involving —COOH group

(i) Reduction:

R—COOH−→−−−−−−(ii)H3O+(i)LiAlH4/etherorB2H6R—CH2—OH1°Alcohol

(ii) Decarboxylation:

R—COO–N+aSodiumcarboxylate−→−−−ΔNaOHandCaOR—H+Na2CO3

(iii) Halogenation:

(Hell-Volhard Zelinsky reaction)

(d) Ring substitution reaction: Aromatic carboxylic acids undergo electrophilic substitution reactions in which —COOH group acts as a deactivating and meta-directing group. They however do not undergo Friedel–Crafts reaction because the carboxyl group is deactivating and the catalyst AlCl3 (Lewis acid) gets bonded to the carboxyl group.

16. Uses of Carboxylic acids:

(i) Formic acid is used in rubber, textile, dyeing, leather and electroplating industry.

(ii) Acetic acid is used as solvent and as vinegar in food industry.

(iii) Adipic acid is used in the manufacture of nylon-6, 6.

(iv) Sodium benzoate is used as preservative.

(v) Higher fatty acids are used for the manufacture of soaps and detergents.

(vi) Esters of benzoic acid are used in perfumery.

17. Some Important Name Reactions

(a) Rosenmund Reduction:

Acid chloride are converted to corresponding aldehydes by catalytic reduction. The reaction is carried out by passing H2 gas through a hot solution of acid chloride in the presence of Pd deposited over BaSO4 (partially poisoned with sulphur or quinoline).

(b) Stephen reaction: Nitriles are reduced to corresponding imines with SnCl2 in the presence of hydrochloric acid, which on hydrolysis give corresponding aldehyde.

SnCl2 + 2HCl → SnCl4 + 2[H]

CH3—C≡≡NEthanenitrile+2[H]+HCl→CH3—CH==NH.HClAcetaldoximehydrochloride−→−H2O(boil)CH3—CHOAcetaldehyde+NH4Cl

(c) Etard reaction: Chromyl chloride oxidises toluene to chromium complex which on hydrolysis gives benzaldehyde.

(d) Gatterman–Koch reaction: When benzene or its derivative is treated with carbon monoxide and hydrogen chloride in the presence of anhydrous AlCl3 and CuCl, it gives benzaldehyde or substituted benzaldehyde.

(e) Friedel–Crafts reactions:

Friedel–Crafts alkylation: Benzene and other aromatic compounds react with alkyl halides in the presence of anhydrous AlCl3 to form alkyl benzenes.

Friedel–Crafts acylation: Benzene and other aromatic compounds react with acylchlorides or acid anhydrides in the presence of anhyd. AlCl3 to form aromatic ketone.

(f) Clemmensen reduction: The carbonyl group of aldehydes and ketones is reduced to CH2 group on treatment with zinc amalgam and concentrated hydrochloric acid.

(g) Wolff–Kishner reduction: The carbonyl group of aldehydes and ketones is reduced to —CH2 group on treatment with hydrazine followed by heating with potassium or sodium hydroxide in a high boiling solvent such as ethylene glycol.

(h) Aldol condensation: Two molecules of aldehydes or ketones containing at least one a-hydrogen atom on treatment with dilute alkali undergo condensation to form b-hydroxy aldehydes (aldol) or b-hydroxy ketones (Ketol).

(i) Cross aldol condensation: When aldol condensation is carried out between two different aldehydes and/or ketones, it is called cross aldol condensation.

( j) Cannizzaro reaction: Aldehydes which do not have an a-hydrogen, undergo self oxidation and reduction (disproportionation) reaction on treatment with concentrated alkali. In this reaction, one molecule of the aldehyde is reduced to alcohol while another is oxidised to carboxylic acid salt.

2HCHOFormaldehyde−→−conc.KOHCH3—OHMethylalcohol+HCOO–K+Potassiumformate

2CH3—C—|CH3|CH3CHO2,2−Dimethylpropanal−→−−NaOH(50%)CH3—C—|CH3|CH3CH2—OH2,2−Dimethylpropanol+CH3—C—|CH3|CH3COO–N+aSodium2,2−dimethylpropanoate

(k) Hell-Volhard-Zelinsky reaction: Carboxylic acids having an a-hydrogen are halogenated at the a-position on treatment with chlorine, or bromine in the presence of red phosphorus to give a-halo-carboxylic acids.

CH3—CH2—COOHPropanoicacid−→−−(ii)H2O(i)Cl2/RedPCH3—CαH|Cl—COOH2−Chloropropanoicacid

18. Chemical Tests for Aldehydes and Ketones

(a) Test for carbonyl group (2, 4-Dinitrophenyl hydrazine test): Both aldehydes and ketones contain carbonyl group. Hence, they react with 2, 4-dinitrophenyl hydrazine to form yellow, or orange precipitate of 2, 4-dinitrophenyl hydrazone.

(b) (i) Tollens’ test: When aldehydes are heated with Tollens’ reagent (ammoniacal silver nitrate solution), they form silver mirror on the inner side of the test tube. Ketones do not respond to this test.

R—CHO+2[Ag(NH3)2]+Tollens’reagent+3OH–→R—COO–+2Ag↓(Silvermirror)+2H2O+4NH3

(ii) Fehling’s test: Aliphatic aldehydes when warmed with a few drops of Fehling’s solution give a reddish brown precipitate of cuprous oxide. Ketones do not respond to this test.

R—CHO+2Cu2++5OH–Fehlingsolution→R—COO–+Cu2O↓Redbrownppt.+3H2O

(iii) Iodoform test: Acetaldehyde, acetone or any ketone having at least one —CH3 group when heated with alkaline solution of iodine form yellow coloured precipitate of iodoform.

2NaOH + I2 → NaOI + NaI + H2O

R—COCH3−→−–NaOH+3NaOIR—COCI3−→−NaOHR—COO–N+a+CHI3↓Iodoform(Yellowppt.)

(c) Tests for Carboxylic Acids

(i) Litmus test: Aqueous solutions of carboxylic acids turn blue litmus red. Phenols also give this test. Alcohols do not respond to this test.

(ii) Sodium bicarbonate test: When carboxylic acid is added to an aqueous solution of sodium bicarbonate, brisk effervescence of CO2 is evolved.

RCOOHCarboxylicacid+NaHCO3→RCOONaSodiumcarboxylate+H2O+CO2↑⏐⏐⏐⏐

Phenols and alcohols do not give this test.

(iii) Ester formation test: On warming carboxylic acids with an alcohol (e.g., ethanol) in presence of a small amount of sulphuric acid, a fruity smell of ester is obtained.

RCOOHCarboxylicacid+ROH′Alcohol−→−H2SO4RCOOR′Ester(FruitySmell)+H2O

(iv) Distinction between formic acid and acetic acid.

Tollens’ reagent test: Formic acid reduces Tollens’ reagent to metallic silver but acetic acid does not.

HCOOHFormicacid+2[Ag(NH3)2]++2OH–→ 2Ag(Silvermirror)⏐↓⏐⏐⏐⏐+CO2↑⏐⏐⏐⏐⏐+2H2O+4NH3

HgCl2 test: Formic acid reduces HgCl2 to give white ppt. of Hg2Cl2 while acetic acid does not give this test.

HCOOHFormicacid+2HgCl2Mercuricchloride→Hg2Cl2↓Mercurouschloride(whiteppt.)+2HCl+CO2↑⏐⏐⏐⏐⏐