BENZOIN

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 1/2 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 deg. c. and the other at 48 deg. c: (th. zmcke, _berichte_, 1871, 4, p. 576). it boils at 306.1 deg. 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 deg. 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]3, melting at 173 deg., 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. benzyl alcohol (phenyl carbinol), c6h5ch2oh, occurs as a benzoic ester in peru balsam, as cinnamic ester in tolu balsam, as acetic ester in essential oil of jasmine, and also in storax. it may be synthetically prepared by the reduction of benzoyl chloride; by the action of nitrous acid on benzylamine; by boiling benzyl chloride with an aqueous solution of potassium carbonate, or by the so-called "cannizzaro" reaction, in which benzaldehyde is shaken up with caustic potash, one half of the aldehyde being oxidized to benzoic acid, and the other half reduced to the alcohol. (_berichte_, 1881, 14, p. 2394). 2c6h5cho + koh = c6h5cook + c6h5ch2oh. it is a colourless liquid, with a faint aromatic smell, and boils at 206 deg. c. on oxidation with nitric acid it is converted into benzaldehyde, whilst chromic acid oxidizes it to benzoic acid. reduction by means of hydriodic acid and phosphorus at 140 deg. c. gives toluene, whilst on distillation with alcoholic potash, toluene and benzoic acid are formed.