__ __ __ __ __ __NH2
/ \_NH.NH _/ \-->NH2 / \_/ \NH2 and NH2 / \_/ \
\__/ \__/ \__/ \__/ \__/ \__/
Hydrobenzene. Benzidine. Diphenylin.
__ __ __ __ __ __
R/ \_NH.NH _/ \--> / \_NH_/ \or R/ \_NH_/ \NH2
\__/ \__/ \__/ \__/ \__/ \__/
Ortho-semidine. Para-semidine.
__NH2__
or / \_/ \NH2.
\__/ \__/
R
BENZOIC ACID, C7H6O2 or C6H5COOH, the simplest representative of the
aromatic acids. It occurs naturally in some resins, especially in gum
benzoin (from _Styrax benzoin_), in dragon's blood, and as a benzyl
ester in Peru and Tolu balsams. It can be prepared by the oxidation of
toluene, benzyl alcohol, benzaldehyde and cinnamic acid; by the
oxidation of benzene with manganese dioxide and concentrated sulphuric
acid in the cold (L. Carius, _Ann_. 1868, 148, p. 51); by hydrolysis of
benzonitrile or of hippuric acid; by the action of carbon dioxide on
benzene in the presence of aluminium chloride (C. Friedel and J.M.
Crafts, _Ann. chim. phys._ 1888 [6], 14, p. 441); by the action of
carbon dioxide on monobrombenzene in the presence of sodium; by
condensing benzene and carbonyl chloride in presence of aluminium
chloride, the benzoyl chloride formed being subsequently hydrolysed; and
similarly from benzene and chlorformamide:--
C6H6 + Cl.CONH2 = HCl + C6H5CONH2,
the benzamide being then hydrolysed. It may also be prepared by boiling
benzyl chloride with dilute nitric acid (G. Lunge, _Berichte_, 1877, 10,
p. 1275); by fusing sodium benzene sulphonate with sodium formate:
C6H5SO3Na + HCO2Na = C6H5COONa + NaHSO3; by heating calcium phthalate
with calcium hydroxide to 330 deg.-350 deg. C.; by heating
benzotrichloride with water in a sealed tube, and from the hippuric acid
which is found in the urine of the herbivorae. For this purpose the
urine is concentrated and the hippuric acid precipitated by the addition
of hydrochloric acid; it is then filtered and boiled for some time with
concentrated hydrochloric acid, when it is hydrolysed into benzoic and
amido-acetic acid. It is made commercially by boiling benzotrichloride
(obtained from toluene) with milk of lime, the calcium benzoate so
obtained being then decomposed by hydrochloric acid
2C6H5CCl3 + 4Ca(OH)2 = (C6H5COO)2Ca + 3CaCl2 + 4H2O.
Benzoic acid crystallizes in glistening leaflets (from water) which melt
at 121.4 deg. C. and boil at 249.2 deg. C. (H. Kopp). Its specific heat
is 0.1946. It sublimes readily and is volatile in steam. It is readily
soluble in hot water and the ordinary organic solvents, but is only
slightly soluble in cold water. When heated with lime, it is decomposed,
benzene being formed; if its vapours are passed over heated zinc dust,
it is converted into benzaldehyde (A. Baeyer, _Ann_. 1866, 140, p. 296).
Distillation of its calcium salt gives benzophenone (q.v.) with small
quantities of other substances, but if the calcium salt be mixed with
calcium formate and the mixture distilled, benzaldehyde is produced. By
the action of sodium amalgam on an aqueous solution of the acid, benzyl
alcohol, tetrahydrobenzoic acid and hexahydrobenzoic acid are formed.
The salts of benzoic acid are known as the benzoates and are mostly
soluble in water. They are readily decomposed by mineral acids with the
production of benzoic acid, and on addition of ferric chloride to their
neutral solutions give a reddish-brown precipitate of ferric benzoate.
Benzoic anhydride, (C6H5CO)2O, is prepared by the action of benzoyl
chloride on sodium benzoate, or by heating benzoyl chloride with
anhydrous oxalic acid (R. Anschutz, _Ann_. 1884, 226, p. 15). It
crystallizes in needles, melting at 42 deg.C., and boiling at 360 deg.
C. It is insoluble in water but readily soluble in alcohol and ether.
Benzoyl chloride, C6H5COCl, is formed by distilling a mixture of
phosphorus pentachloride and benzoic acid; by the action of chlorine on
benzaldehyde, or by passing a stream of hydrochloric acid gas over a
mixture of benzoic acid and phosphorus pentoxide heated to 200 deg. C.
(C. Friedel, _Ber._ 1869, 2, p. 80). It is a colourless liquid of very
unpleasant smell, which boils at 198 deg. C., and solidifies in a
freezing mixture, the crystals obtained melting at -1 deg. C. It shows
all the characteristic properties of an acid chloride.
Ethyl benzoate, C6H5COOC2H5, is best prepared by boiling benzoic acid
and alcohol with a small quantity of sulphuric acid for some hours (E.
Fischer and A. Speier, _Berichte_, 1896, 28, p. 3252). It is a
colourless liquid of boiling point 213 deg. C.
_Benzamide_, C6H5CONH2, is prepared by the action of benzoyl chloride on
ammonia or ammonium carbonate, or from ethyl benzoate and ammonia. It
crystallizes (from water) in glistening leaflets which melt at 130 deg.
C. and boil at 288 deg. C. Its silver salt behaves as if it were the
salt of an imido benzoic acid, since it yields benzimido ethyl ether
C6H5.C( : NH).OC2H5 with ethyl iodide (J. Tafel and C. Enoch,
_Berichte_, 1890, 23, p. 1550).
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 deg. 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
deg. C. and boiling at 343-344 deg.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 deg. 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 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).