Chemistry Library

Pyruvic acid Pyruvic acid ( acetylformic acid, pyroracemic acid, a-ketopropionic acid, 2-oxopropanoic acid ), b.p. 165 o C, is the simplest keto acid. It may be prepared: 1. By heating tartaric acid alone, or better, with potassium hydrogen sulphate at 210-220 o C. The reaction is believed to take place via the formation of hydroxymaleic acid (shown in below figure 1), which rearranges to oxalacetic acid, (shown in Figure II) This is the best method for preparing pyruvic acid, and it was this method which gave rise to the name pyroracemic acid. 2 Other methods of preparation are the oxidation of lactic (a-hydroxypropionic) acid, the hydro-lysis of a,a-dibromopropionic acid or acetyl cyanide, e.g., CH 3 COCl     (KCN)   ⟶      CH 3 COCN     (H + ) ⟶      CH 3 COCO 2 H A general method of preparing a-keto-acids uses the Claisen condensation between ethyl oxalate and monocarboxylic esters: Pyruvic acid behaves as a ketone and as an acid; it forms a

Acid Acid or acyl chlorides may be prepared by the replacement of the hydroxyl in the carboxyl group by chlorine, are also known as acyl chlorides because they contain the acyl group. Nomenclature According to the I.U.P.A.C. system the class suffix of the acyl chlorides is –oyl; the common names are formed by changing the suffix-ic of the trivial name of the acid into –yl, e.g., CH 3 COCl                                             (CH 3 ) 2 CHCOCl Ethanol chloride                              2-methylpropanoyl chloride Acetylchloride                                  isobutyryl chloride If the carboxyl group is considered as a substituent, then according to the I.U.P.A.C. system the nomenclature of all substances containing acyl groups is in all cases based on the name ‘carbonyl’ for the CO group. e.g., CH 3 CH 2 CH 2 COCl                               propane-1-carbonyl chloride When naming amides, the ‘yl’ is elided before the suffix amide, e.g., CH 3

Ester Esters are compounds which are formed when the hydroxylic hydrogen atom in oxygen acids is replaced by an alkyl group; the acid may be organic or inorganic. The most important esters are derived from the carboxylic acids. The general formula of the carboxylic esters is C n H 2n O 2 , which is the same as that of the carboxylic acids, and they are named as the alkyl salts of the acid, e.g., CH 3 COOC 2 H 5                                     ethyl acetate (CH 3 ) 2 CHCOOCH(CH 3 ) 2                  isopropyl isobutyrate Carboxylic esters are formed by the action of the acid on an alcohol: Acid  +  Alcohol    ⇌    ester  +  water The reaction is reversible, the forward reaction being known as esterification, and the backward reaction as hydrolysis. General method of preparation of the carboxylic esters 1.  The usual method is esterification. The reaction is always slow, but is speeded up by the presence of small amounts of inorganic acids as catalysts, e.

Formic Acid Formic acid is also known as methanoic acid. Formic acid is a pungent corrosive liquid, m.p. 8.4 o C, b.p. 100.5 o C, miscible in all proportions with water, ethanol and ether. It forms salts which, except for the lead and silver salts, are readily soluble in water. Formic acid is a stronger acid than any of its homologues. Preparation of Formic acid Formic acid is prepared industrially by heating sodium hydroxide with carbon monoxide at 210 o C, and at a pressure of 6-10 atmospheres: NaOH    +    CI     ⟶       HCO 2 Na An aqueous solution of formic acid is obtained by distilling the sodium salt with dilute sulphuric acid: 2HCO 2 Na    +    H 2 SO 4       ⟶       2HCO 2 H    +    Na 2 SO 4 Anhydrous formic acid is obtained from the aqueous solution (70-77 per cent) by the addition of butyl formate followed by distillation. The first fraction is an azeotrope of ester and water, and then the excess of ester is removed from the formic acid by fraction

 Acetone Acetone is also known as dimethyl ketone, propan-2-one. Acetone is a colorless, pleasant-smelling liquid, b.p. 56 o C, miscible with water, ethanol and ether in all proportions. Preparation of Acetone Acetone is prepared industrially: 1. By the catalytic dehydrogenation (Cu or ZnO) or catalytic oxidation (Ag) of isopropanal. 2. by passing a mixture of propene and oxygen, under pressure, into an aqueous solution of palladium and cupric chlorides ( cf . acetaldehyde). 3. Acetone is also manufactured by the oxidation of natural gas, and is obtained as a by-product in the oxidation of cumene to phenol. Although acetone does not exist as a hydrate in water, it nevertheless undergoes reversible hydration. On the other hand, Wilson et al. (1963) gave shown that acetone hydrate exists in the solid state. Ketones do not polymerise, but readily undergo condensation reactions. Acetone readily forms mesityl oxide, phorone and diacetone alcohol, but in additio

Chloral Chloral is also known as trichloroacetaldehyde. Chloral is a colorless, oily, pungent-smelling liquid, b.p. 98 o C, soluble in water, ethanol and ether. Preparation of chloral Chloral is prepared industrially by the chlorination of ethanol. Chlorine is passed into cooled ethanol, and then at 60 o C, until no further absorption of chlorine takes place. The final product is chloral alcoholate, CCl 3 CH(OH)OC 2 H 5 , which separates out as a crystalline solid which, on distillation with concentrated sulphuric acid, gives chloral. When heated with concentrated potassium hydroxide, it yields pure chloroform: Chloral is oxidized by concentrated nitric acid to trichloroacetic acid and is reduced by aluminium ethoxide to trichloroethanol. CCl 3 CO 2 H     (HNO 3 ) -     CCl 3 CHO     Al(OC 2 H 5 ) 3 -     CCl 3 CH 2 OH Chloral undergoes the usual reactions of an aldehyde, but its behavior towards water and ethanol is unusual. When chloral is treated with wate

Condensation reactions of formaldehyde Formaldehyde or methanal  is a colorless, pungent-smelling gas, b.p. -21 o C, extremely soluble in water. It is powerful disinfectant and antiseptic. Formaldehyde can participate in the ‘crossed’ Cannizzaro reaction, and the nature of the final product depends on the structure of the other aldehyde. Aldehydes with no  α-hydrogen atoms readily undergo the crossed Cannizzaro reaction; e.g ., benzaldehyde forms benzyl alcohol: C 6 H 5 CHO   +   HCHO   +   NaOH    ⟶    C 6 H 5 CH 2 OH   +   HCO 2 Na Aldehydes with one α-hydrogen atom react as follows: This β-hydrxyaldehyde in the presence of excess of formaldehyde forms a substituted trimethylene glycol: Thus the first step in the above reaction is the replacement of the α-hydrogen atom by a hydroxymethyl group, CH 2 OH, and the second step is the crossed Cannizzaro reaction. In a similar manner, aldehydes with two  α-hydrogen atoms are converted first into the hydrox

Acetaldehyde Acetaldehyde is also known as ethanol. Acetaldehyde is a colorless, pungent-smelling liquid, b.p. 21 o C, miscible with water, ethanol and ether in all proportions. Preparation of acetaldehyde Acetaldehyde is prepared industrially: 1.  By the dehydrogenation or air oxidation of ethanol in the presence of a silver catalyst at 300 o C ( cf . formaldehyde): CH 3 CHO    +    H 2    (Ag)   ⟵      CH 3 CH 2 OH     (air+Ag)   ⟶     CH 3 CHO     +   H 2 O 2.  By the hydration of acetylene. This method is decreasing in importance. 3.  By passing a mixture of ethylene and oxygen, under pressure, into an aqueous solution of palladium and cupric chlorides at 50 o C. CH 2 =CH2   +   PdCl 2    +   H 2 O    ⟶     CH 3 CHO   +   Pd   +   2HCl                         2CuCl 2    +   Pd    ⟶    2CuCl   +   PdCl 2     2CuCl   +   2HCl   +   1/2O 2   ⟶     2CuCl 2    +   H 2 O Polymers of acetaldehyde 1.  When acetaldehyde is treated with a few drops of co

Formaldehyde Formaldehyde is also known as methanal. Formaldehyde is a colorless, pungent-smelling gas, b.p. -21 o C, extremely soluble in water. It is powerful disinfectant and antiseptic. Preparation of formaldehyde Formaldehyde is prepared industrially: 1.  BY the dehydrogenation or air oxidation of methanol in presence of a silver catalyst at 400 o C: CH 2 O   +  H 2     (Ag) ⟵     CH 3 OH    (air+Ag)   ⟶      CH 2 O   +   H 2 O In the oxidation method, the condensate obtained is a mixture of formaldehyde, methanol and water. It is freed from excess of methanol by distillation, and the resulting mixture is known as formalin (40 per cent formaldehyde, 8 per cent methanol, 52 per cent water). 2.  By the air oxidation of methane or propane-butane mixtures (from natural gas) in the presence of various metallic oxides. Reactions of Formaldehyde Formaldehyde undergoes many of the general reactions of aldehydes, but differs in certain respects. When treated w

Ketones Ketones have the general formula C n H 2n O and it contain the oxo (carbonyl) group. In Ketones both available valencies are attached to carbon atoms and so the keto group occurs within a chain ( cf . ketens). Nomenclature The lower members are commonly named according to the alkyl groups attached to the keto group, e.g., CH 3 COCH 3                             dimethyl ketone CH 3 CH 2 COCH(CH 3 ) 2            ethyl isopropyl ketone The positions of side-chains or substituents are indicated by Greek letters, the α-carbon atom being the one adjacent to the keto group, e.g., CH 3 CHClCOCH 2 CH 2 Cl                      α ,β’-dichlorodiethyl ketone If the two alkyl groups in a ketone are the same, the ketone is said to be simple or symmetrical; if unlike, mixed or unsymmetrical ( cf . ethers). According to I.U.P.A.C. system of nomenclature, ketones are designated by the suffix –one, which is added to thename of the hydrocarbons from which they are de

Aldehydes Aldehydes have the general formula C n H 2n O and it contain the oxo (carbonyl) group. In aldehydes, the functional group is –CHO, i.e., one of the available valencies of the carbonyl group is attached to hydrogen, and so the aldehyde group occurs at the end of a chain. Nomenclature The lower members are commonly named after the acids that they form on oxidation. The suffix of the names of acids is –ic (the names of the trivial system are used); this suffix is deleted and replaced by aldehyde, e.g.,         HCHO              (O ) ⟶       HCO 2 H Formaldehyde                        formic acid (CH 3 ) 2 CHCHO           (O) ⟶           (CH 3 ) 2 CHCO 2 H Isobutyraldehyde                                     isobutyric acid The positions of side-chains or substituents are indicated by Greek letters, the α carbon atom being the one adjacent to the aldehyde group, e.g., According to the I.U.P.A.C. system of nomenclature, aldehydes are designated b