Chlor-, brom-, iodo- and fluor-benzoic acids are known and can be obtained by oxidizing the corresponding halogen toluenes, or from the amido acids, or by substitution. Nitration of benzoic acid gives chiefly meta-nitro-benzoic acid. The ortho- and para-nitro-benzoic acids can be obtained by oxidizing ortho-and para-nitro-cinnamic acids. Ortho-amino-benzoic acid, C6H4·NH2·COOH (anthranilic acid), is closely related to indigo (q.v.).
Gum benzoin, which contains from 12 to 20% of benzoic acid, is used in medicine as the essential constituent of benzoated lard, Adeps benzoatus, which owes its antiseptic properties to benzoic acid; and in friar’s balsam, Tinctura benzoini composita, which is an ancient and valuable medicament, still largely used for inhalation in cases of laryngitis, bronchitis and other inflammatory or actually septic conditions of the respiratory tract. It owes its value to the benzoic acid which it contains. A fluid drachm of friar’s balsam may be added to a pint of water at a temperature of about 140° F., and the resultant vapour may be inhaled from the spout of a kettle or from a special inhaler. Benzoic acid itself, ammonium benzoate and sodium benzoate are all administered internally in doses of from five to thirty grains. The ammonium salt is most often employed, owing to the stimulant character of the ammonium base. The acid itself is a powerful antiseptic. When administered internally, it causes the appearance of hippuric acid in the urine. This is due to its combination in the body with glycocoll. The combination probably occurs in the kidney. The hippuric acid in the urine acts as a stimulant and disinfectant to the urinary mucous membrane. Benzoic acid is also excreted by the bronchi and tends to disinfect and stimulate the bronchial mucous membrane. Hence the value of friar’s balsam. The acid and its salts are antipyretic and were used in Germany instead of salicylates in rheumatic fever. But the most important fact is that ammonium benzoate is largely used—often in combination with urinary anodynes such as tincture of hyoscyamus—as a urinary antiseptic in cases of cystitis (inflammation of the bladder) and pyelitis (inflammation of the pelvis of the kidney).
BENZOIN, C6H5CHOH·CO·C6H5, a ketone-alcohol, which may be prepared by boiling an alcoholic solution of benzaldehyde with potassium cyanide; by reducing benzil (C6H5CO·CO·C6H5) with zinc and acetic acid; or by the oxidation of hydrobenzoin (C6H5-CHOH-CHOH-C6H5). It is a colourless, crystalline solid, readily soluble in alcohol and ether, melting at 137° C. and boiling at 343-344° C. On passing the vapour of benzoin over heated lead oxide, it is converted into benzil and benzophenone. Owing to the readiness with which it is oxidized, it acts as a reducing agent, giving a red precipitate of cuprous oxide with Fehling’s solution in the cold. Chlorine and nitric acid oxidize it to benzil; chromic acid mixture and potassium permanganate, to benzoic acid and benzaldehyde. On heating with zinc dust, desoxy-benzoin (C6H5CO·CH2·C6H5) is obtained; sodium amalgam converts it into hydrobenzoin; and fuming hydriodic acid at 130° C. gives dibenzyl (C6H5CH2·CH2·C6H5). By fusion with alkali it is converted into benzil; and with an alcoholic solution of benzaldehyde in presence of ammonia it forms amarine (triphenyl dihydro-glyoxaline). In the presence of sulphuric acid it condenses with nitriles to oxazoles (q.v.).
BENZOIN, or Gum Benjamin (supposed to be from Arab. luban, frankincense, the first syllable being dropped in Romanic as if it were the article), a balsamic resin obtained from Styrax benzoin, a tree of considerable size, native to Sumatra and Java, and from other species of Styrax. It is obtained by making incisions in the bark of the trees, and appears to be formed as the result of the wound, not to be secreted normally. There are several varieties of benzoin in commerce: (1) Siam benzoin, which apparently does not come from Styrax benzoin, is the finest and most aromatic, and occurs in the form of small “tears,” rarely exceeding 2 in. in length by ½ in. in thickness, and of “blocks” made up of these tears agglomerated by a clear reddish-brown resin. The odour of Siam benzoin is partly due to the presence of vanillin, and the substance contains as much as 38% of benzoic acid but no cinnamic acid. (2) Sumatra benzoin occurs only in masses formed of dull red resin enclosing white tears. It contains about 20% of cinnamic acid in addition to 18 or even more of benzoic. (3) Palembang benzoin, an inferior variety, said to be obtained from Styrax benzoin in Sumatra, consists of greyish translucent resinous masses, containing small white opaque tears. It does not appear to contain cinnamic acid. Large quantities of benzoin are used as incense. Its medicinal uses depend on the contained benzoic acid (q.v.).
BENZOPHENONE (Diphenyl Ketone), C6H5·CO·C6H5, the simplest representative of the true aromatic ketones. It may be prepared by distilling calcium benzoate; by condensing benzene with benzoyl chloride in the presence of anhydrous aluminium chloride; by the action of mercury diphenyl on benzoyl chloride, or by oxidizing diphenylmethane with chromic acid. It is a dimorphous substance existing in two enantiotropic forms, one melting at 26° C. and the other at 48° C: (Th. Zmcke, Berichte, 1871, 4, p. 576). It boils at 306.1° C., under a pressure of 760.32 mm. It is reduced by sodium amalgam to benzhydrol or diphenyl carbinol C6H5·CHOH·C6H5; a stronger reducing agent, such as hydriodic acid in the presence of amorphous phosphorus converts it into diphenylmethane (C6H5)2·CH2. Potash fusion converts it into benzene and benzoic acid. With phenylhydrazine it forms a hydrazone, and with hydroxylamine an oxime, which exists in one form only; if, however, one of the phenyl groups in the oxime be substituted in any way then two stereo-isomeric oximes are produced (cf. Stereo-Isomerism); thus parachlorbenzophenone oxime exists in two different forms (V. Meyer and K.F. Auwers, Berichte, 1890, 23, p. 2403). Many derivatives are known, thus ortho-amino-benzophenone, melting at 106° C., can be obtained by reduction of the corresponding nitro compound; it condenses under the influence of heated lead monoxide to an acridine derivative and with acetone in presence of caustic soda it gives a quinoline. Tetramethyl-diamido-benzophenone or Michler’s ketone, CO[C6H4N·(CH3)2]2, melting at 173°, is of technical importance, as by condensation with various substances it can be made to yield dye-stuffs. It is prepared by the action of carbonyl chloride on dimethyl aniline in the presence of aluminium chloride: COCl2 + 2C6H5N(CH3)2 = 2HCl + CO[C6H4N(CH3)2]2.