CHCH2.OH at 252°. Chromic acid oxidises tollylene glycol to terephthalic acid. Phenyl Alkylenes. 1042. Styrolene, cinnamene, or phenyl ethylene : CgHgC6H5.CH:CH2, is a constituent of liquid storax, from which it can be obtained by distillation with water as a thin oil, boiling at 145° and of sp. gr. 924°. It can be prepared by heating cinnamic acid with lime : CHẸCH:CH.CO.OH + CaO = CaCO, + C,H,CH:CH,; by boiling phenethyl chloride (§ 1029) with alcoholic potassic hydrate: C6H5.CH2.CH2.Cl + KOH = KCl + H2O + C6H5.CH:CH2; and, together with benzene, by the action of a red heat on acetylene. On long standing, or more quickly at 200°, it polymerises to an amorphous, transparent solid, metastyrolene, which is again converted into styrolene on distillation. It unites directly with the halogens, forming styrolene dihaloids. Styrolene dichloride, C ̧H ̧Cl2 = C6H5.CHCI.CH2Cl, is liquid; the dibromide, CH,Br2, crystallises in plates and needles melting at 68°-69°. They both decompose on heating, either alone or with strong bases, into a-chlor-styrolene, C6H5.CH:CHCl, and a-brom-styrolene, CH.CH: CHBr, liquids which cannot be distilled unaltered. The isomeric B-halogen styrolenes are formed by the dry distillation of phenyl-chlor- and phenyl-brom-lactic acids (§ 1096). B-Chlor-styrolene, CH5.CC:CH2, is an oil boiling at 199°, of hyacinth-like odour; B-brom-styrolene, CH5.CBr:CH2, boils at 228°. Styrolene diiodide, CH,I2, is formed by mixing styrolene with solution of iodine in potassic iodide; it cannot be preserved, as it decomposes readily into iodine and metastyrolene. On heating styrolene dibromide or a-brom-styrolene with alcoholic potassic hydrate at 120° Phenyl acetylene, or acetenyl benzene, С ̧H ̧ = C6H5.C¦ CH (comp. §759), is obtained as a colourless oil boiling at 140°. 8 Like acetylene, allylene, &c., it can exchange the hydrogen atom of the C.H group for metal; with ammoniacal cuprous chloride it gives a yellow precipitate, (C.H5)2Cu2; with ammoniacal silver solutions, a white precipitate of CH5.CC.Ag.AgO; with metallic soCH.CC.Ag.Ag. dium hydrogen is evolved, and a white substance, sodium phenyl acetylene, CH5.C: CNa, produced, which is spontaneously inflam mable in air. The silver and copper compounds give phenyl acetylene when treated with hydrochloric acid. On shaking the copper compound with air in presence of alcoholic ammonia, diacetenyl phenyl, C16H109 is formed: C6H5.CC.Cu | +02 = 2CuO + C&H.C C CH.C: This latter crystallises in long brittle needles, melting at 97° and insoluble in water. 1043. Homologues of Styrolene.-a-Phenyl propylene : is formed in small quantity, together with phenyl-propyl alcohol, by treatment of cinnamic alcohol with sodium amalgam. It is a colourless oil, boiling between 165° and 170°, and unites with bromine to form a crystalline dibromide, C,H10Br2, crystallising at 66.5°. B-Phenyl propylene, or allyl benzene : C9H10=C6H5.CH2.CH:CH2, is obtained by heating allylic bromide with benzene and zinc dust. It is a liquid boiling at 155°. Phenyl butylene, C10H12, can be prepared synthetically by the action of sodium on benzylic chloride and allylic iodide : CH.CH,Cl+I.CH2.CH:CH2 + Na, NaCl + NaI = = + C6H5.CH.CH2.CH:CH2. It is a colourless oil, boiling between 176° and 178° and giving a liquid dibromide. 621 AROMATIC ACIDS, CnH2n-8O2 = CnH2n' - 7.CO.OH, 1044. The aromatic acids of the formula CnH2n-802 fall naturally into two chief groups. 1. Aromatic acids proper, in which the CO.OH group is directly united to the carbon of the benzene nucleus. These comprise the first member of the series, benzoic acid : C2H6O2 = C6H5.CO.OH, and its alkyl substitution products: C.H, {Count', CH, {C.Hm+1)2, 4 CO.OH &c. 2. Aromatised fatty acids, in which a hydrocarbon group, CH2n is placed between the benzene nucleus and the CO.OH group. They may be regarded as derivatives of the fatty acids, CnH2n+1.CO.OH, in whose alkyl group a hydrogen atom has been replaced by a benzene nucleus. This latter can either be phenyl or an alkyl-substituted phenyl. In these ways the number of possible isomers becomes very large, as shown by the following list of acids of the formula C,H1002 :— CHCH Aromatic Acids. CH, {C3. ethyl benzoic acid, 3 varieties, o., p., m. CO.OH (CH3)2 CH, {C.) dimethyl benzoic acid, 6 varieties. CO.OH C.H,.CH.CO.OH C6H5.CH2.CH2.CO.OH, B-phenyl propionic acid. CH, {CH.CO.OH methyl-phenylacetic acid, 3 varieties, o., p., and m. The hydrocarbon groups united to CO.OH can have their hydrogen substituted for other elements or radicals, whilst the acid group CO.OH is capable of all those metamorphoses previously mentioned (comp. § 535), yielding salts, acid anhydrides, halogen and nitrogen derivatives, &c. 1045. Formation of Aromatic Acids. In addition to the oxyda tion of the corresponding aldehydes, alcohols, and alkylised benzenes (§ 1009), the aromatic acids can be formed by a series of synthetic processes, which, for the aromatised fatty acids, completely agree with those for the synthesis of the fatty acids themselves (comp. § 559), and are somewhat similar for benzoic acid and its alkyl substitutes, though somewhat modified by the nature of the benzene nucleus. The most important of them may be classified as follows, according to the materials employed as starting points: 1. The halogen substitution products of the aromatic hydrocarbons, especially the bromine compounds, yield a. Alkyl salts, when mixed with alkyl chloro-carbonates, treated with sodium amalgam, and gently heated; e.g. CHBr + Cl.c0.0.C.H. + Na,= NaBr + NaCl b. Sodic salts of aromatic acids when carbonic anhydride is led into their ethereal solutions, which are at the same time treated with sodium; e.g. C6H4 Br 2. The aromatic sulphonic acids exchange the group SO2.OH for CO.OH a. By heating their alkaline salts with alkaline formates; e.g. C.H.SO,OK + KO.CHO = K,SO3 + CH.CO.OH. b. By dry distillation with potassic cyanide, when aromatic cyanides (the nitriles of the acids) are first formed; e.g. C&H CH CH, + KCN = K.SO + CHỊCH 4.SO2.OK · K2SO3 which, like all true cyanides, are converted by bases or acids in the presence of water into ammonia and aromatic acids (comp. § 558, 3). 3. These same nitriles are formed by long heating of aromatic isocyanides to temperatures of 200° and above: CH5.N CCH.C: N, and by desulphurising the isosulpho-cyanates by heating with powdered copper: CH.N:C:S+ Cu2 = Cu2S + C6H5.CN. 1046. By dry distillation of a mixture of the salt of an aromatic acid with a strong base, the CO.OH group is exchanged for hydrogen, and a hydrocarbon containing one atom of carbon less is obtained. This process occurs most readily when calcic salts are heated with calcic hydrate; e.g. (C6H5.CO.O)Ca + Ca(OH)2 = 2CaCO3 + 2C6H6 [C6H3(CH3)2CO.O],Ca + Ca(OH)2 = 2CaCO3 + 2C,H,(CH3)2′ Dry distillation of the calcic salts with calcic formate converts them into the corresponding aldehydes (§ 386), which can be further converted into the primary alcohols. BENZOIC ACID, C7H6O2 = C6H5.CO.OH. 1047. Benzoic acid occurs in several resins, either free or in the form of ethereal salts (e.g. in gum benzoïn, from Styrax Benzoin), and at times it occurs naturally in the urine of herbivorous animals. It is obtained synthetically by the oxidation of benzoic aldehyde, the monalkyl benzenes (§ 1009)-for instance, toluene-and the whole of the aromatised fatty acids with non-substituted phenyl groups: = C6H5.CnH2n-CO.OH + 3n0nCO2 + nH2O + С¿H5.CO.OH. It can be prepared, by the general methods already given, from brom-benzene, benzene-monosulphonic acid, and phenyl isosulphocyanide. It is obtained in small quantity by the oxidation of albuminoids or of benzene, either alone or mixed with formic or oxalic acids. The chief source of the benzoic acid occurring in commerce is hippuric acid, or benzoyl-glycocine, a substance occurring in the urine of herbivorous Mammalia; on boiling with acids or alkalies, or by putrid fermentation, this is resolved into glycocine and benzoic acid or their respective salts (comp. § 717). It is best obtained from gum benzoïn by slow heating in a flat iron pan lightly covered with filter paper and having a paper hood. The vapours of the acid pass through the filter paper and condense on the paper hood in needles. It is purified by recrystallisation from boiling water, resublimation or distillation with water. Benzoic acid crystallises in shining, colourless, flexible, flattened needles or leafy crystals, melting at 120° and volatilising with water vapour below 100°; it boils at 250°. At ordinary temperatures it has a pleasant aromatic odour, but when its vapour is more freely evolved it produces coughing. It dissolves in about 200 parts of cold and 24 parts of boiling water, in two parts cold and 1 part boiling absolute alcohol, and readily also in ether, benzene, and oils. By action of sodium amalgam on an aqueous solution of benzoic acid this is partly reduced to benzylic alcohol, whilst at the same time, together with other bodies, a hydrogen addition product, benzoleïc acid, C-H1002 == C6H,.CO.OH, is formed, as an oil which is oxidised by atmospheric oxygen, again yielding benzoic acid. 1048. The salts of benzoic acid, the benzoates, are mostly readily soluble in water and crystallisable. Their dilute aqueous solutions give with ferric chloride an amorphous reddish brown precipitate of basic ferric benzoate. The alkali salts are very readily soluble in water. C,H,KO2,3H2O and C,H,NaO2, H2O crystallise in needles, frequently united to tufts; (C-H5O2)2Bа,3H2O and 5 (C7H5O2)2Ca,2H2O are also readily soluble; (C-H5O2)2Pb,H2O and C,H,AgO, are crystalline powders, difficultly soluble in cold water. The ethereal salts of benzoic acid are obtained similarly to those of the fatty acids. Methylic benzoate, CH5.CO.O.CH3, boiling at 199°, and ethylic benzoate, boiling at 211°, are colourless liquids, heavier than water, of agreeable odour. Benzylic benzoate : C6H5.CO.O.CH2.C6H5, |