BENZIDINE (DIPARA-DIAMINO-DIPHENYL), NH2

This article appears in Volume V03, Page 756 of the Encyclopedia Britannica.

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BENZIDINE (DIPARA-DIAMINO-DIPHENYL), NH2 C6H4 C6H4 NH2, a chemical base which may be prepared by the reduction of the corresponding dinitro-

diphenyl

DIPHENYL (phenyl benzene), C6H5

, or by the reduction of azobenzene with tin and hydrochloric acid. In this latter case hydrazo-benzene C6H5NHNHC6H5 is first formed and then undergoes a peculiar re-arrangement into

benzidine

BENZIDINE (DIPARA-DIAMINO-DIPHENYL), NH2

(see H. Schmidt and G. Schultz, Annalen, 1881, 207, p. 320; O. N. Witt and Hans v. Helmont, Berichte, 1894, 27, p. 2352; P. Jacobson, Berichte, 1892, 25, p. 994).

Benzidine

BENZIDINE (DIPARA-DIAMINO-DIPHENYL), NH2

crystallizes in plates (from water) which melt at 122 C., and boil above 36o C., and is characterized by the

great

GREAT

insolubility of its sulphate. It is a di-acid base and forms salts with the

mineral

MINERAL

acids. It is readily
brominated and nitrated; when the nitration is carried out in the presence of sulphuric acid, the nitro-groups take up the meta position with regard to the amino-groups. Benzidine finds commercial application since its tetrazo compound couples readily with amino-sulphonic acids, phenol carboxylic acids, and phenol and naphthol-sulphonic acids to produce substantive

cotton

COTTON
COTTON (Fr. coton; from Arab. qutun)
COTTON, CHARLES (163o–1687)
LYNCH
- LYNCH, PATRICIO (1825–1886)
_181.html">COTTON, GEORGE
EDWARD
- EDWARD
LYNCH
- LYNCH, PATRICIO (1825–1886)
(1813–1866)
COTTON, JOHN (1585–1652)
COTTON, SIR ROBERT BRUCE

dyes (see DYEING). Among such dyestuffs are chrysamine or flavophenine, obtained from salicylic acid and diazotized benzidine, and congo red obtained from sodium naphthionate and diazotized benzidine. On the constitution of benzidine see G. Schultz (Annalen, 1874, 174, p. 227).
The Benidine and Semidine

Change

CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

.Aromatic hydrazo compounds which contain free para positions are readily converted by the action of acids, acid chlorides and anhydrides into

diphenyl

DIPHENYL (phenyl benzene), C6H5

derivatives; thus, as mentioned above, hydrazobenzene is converted into benzidine, a small quantity of diphenylin being formed at the same time. The two products are separated by the different solubilities of their sulphates. This reaction is known as the benzidine transformation. If, however, one of the para positions in the hydrazo compound is substituted, then either diphenyl derivatives or azo compounds are formed, or what is known as the semidine

change

CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

takes place (P. Jacobson, Berichte, 1892, 25, p. 992; 1893, 26, p. 681; 1896, 29, p. 268o; Annalen, 1895, 287, p. 97; 1898, 303, p. 290). A para mono substituted hydrazo compound in the presence of a hydrochloric acid solution of stannous chloride gives either a para diphenyl derivative (the substituent group being eliminated), an ortho-semidine, a para-semidine, or a diphenyl base, whilst a decomposition with the formation of amines may also take place. The nature of the substituent exerts a specific influence on the reaction; thus with chlorine or bromine, ortho-semidines and the diphenyl bases are the

chief

CHIEF (from Fr. chef, head, Lat. caput)

products; the dimethylamino, -N(CH3)2, and acetamino, -NHCOCH3, groups give the diphenyl base and the para-semidine respectively. With a methyl group, the

chief

CHIEF (from Fr. chef, head, Lat. caput)

product is an ortho-semidine, whilst with a carboxyl group, the diphenyl derivative is the chief product. The ortho- and para- semidines can be readily distinguished by their behaviour with different reagents; thus with nitrous acid the ortho-semidines give azimido compounds, whilst the para-semidines give complex diazo derivatives; with formic or acetic acids the ortho-semidines give anhydro compounds of a basic character, the para-semidines give acyl products possessing no basic character. The carbon disulphide and salicylic aldehyde products have also been used as means of distinction, as has also the formation of the stilbazonium bases obtained by condensing ortho-semidines with benzil (0. N. Witt, Berichte, 1892, 25, p. 1017).
Structurally we have:
NH2
-NHNH( > j NH2<)< >NH2 and NH2 < ><% Hydrazohenzene. Benzidine. Diphenylin.
NH2
R< >NHNH< > > < )NH<----> or RK > NH NH_,
R
Ortho-semidine. Para-semidine.
NH2
or( >< )NIH2. R

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