PREPARATION LXVII. Ethylmalonic Acid.-In those compounds in which the group CO.CH, CO occurs (Prep. LXI.), both H atoms are successively replaceable by Na. If ethylmalonic ether were acted on by a second atom of sodium and a second molecule of alcohol iodide both H atoms would be replaced by alcohol radicals. It is possible in this way to build up a series of homologous dibasic acids. Note that dibasic acids with both carboxyl groups attached to the same C atom readily lose CO, on heating and form the monobasic acid. PREPARATION LXX. Ethyl Diethoxalate.-This reaction of Frankland and Duppa consists, in the first place, in the formation of zinc ethyl (by the action of zinc on ethyl iodide), and this reacting on the acid ether replaces the O atom of the one carbonyl group by two (it can also replace it by one) alcohol radicals. The reaction is applicable to ethers of monobasic acids, but not to the homologues of oxalic ether, CnH2 - 204. A similar reaction occurs in the case of aldehydes, ketones, and acid chlorides. PREPARATIONS LXXI. AND LXXII. Formic Acid and Allyl Alcohol.-Note the different action of oxalic acid on glycerin at different temperatures. The reducing action of formic acid on mercury and silver salts is due to the aldehyde character of the acid, (OH).COH. PREPARATION LXXIII. Allyl Iodide.-This reaction is due to the action of HI, or, what amounts to the same, the combined action of iodine and phosphorus on glycerin. It is probable that propenyl triiodide is first formed, CH,I.CHI.CH,I, which decomposes into CH, CH.CH.I + I. With an excess of HI allyliodide is further transformed into propylene, CH2 : CH.CH2I + HI=CH: CH.CH, + I, and isopropyl iodide, CH: CH.CH3 + HI= CH3.CHI.CH3. PREPARATION LXXIV. Propenyl Tribromide.-The bromine has a two-fold action. It acts in the first place by addition, as in the case of ethylene bromide (Prep. L.), and in the second place by substitution replacing the atom of I. PREPARATION LXXVI. Glyceric Acid.-Note the oxidation of the carbinol group CH2(OH) to carboxyl (CO2H) characteristic of primary alcohols. PREPARATION LXXIX. Urea.-Further properties of urea are as follows: It decomposes above its melting-point into biuret and cyanuric acid. Boiled with alkalis, or heated gently with conc. sulphuric acid, it takes up the elements of water, giving off NH, and CO2. It undergoes similar decomposition in putrefying urine. It combines with acids, bases, and salts to form crystallisable compounds. The nitrate and the compound, obtained by adding a solution of mercuric nitrate to urea, are characteristic. PREPARATION LXXXII. Alloxan.-The constitution of alloxan has been determined by the following reactions amongst others. It decomposes with caustic soda or potash into mesoxalic acid and urea. It combines with hydroxylamine to form violuric acid (presence of carbonyl group). On further oxidation with dilute nitric acid it loses CO, and yields parabanic acid (oxalyl urea), the constitution of which has been synthetically determined. |