THE CHEMICAL NEWS,

VOL. CXXVII. No. 3304.

PERCHROMIC ACID.

BY GEOFFREY N. RIDLEY.

I.-FORMULE.

Perchromic acid has been given two formulæ-HCrO, and H,CrO,. It therefore deviates from the path followed by its "relative," permanganic acid, whose formula is given as HMnO or H,Mn,O,. The equation representing the formation of the acid by the interaction of chromic acid and hydrogen peroxide may be written thus:

4

2H,CrO, +7H2O2 = 2H,Crо ̧ + 6H20. This reaction occurs when the hydrogen peroxide is in excess. Otherwise, acid corresponding to the probable formula HCrO, is produced. In the hypothetical case of the formula for perchromic acid being H.Cr2O, the formation of the compound may be expressed thus: 2H2CrO + H2O2 H2Cr2O, + 2H2O. It has been suggested that chromium may form an octovalent compound, perchromic acid consisting of a combination of Cr2O, with H2O2, or Cro, with H2O.

=

8

As regards the decomposition of perchromic acid by water, the action is slow and only brought about in a short space of time by much shaking. The acid is gradually removed from the ether colouring the water a pale purple, which readily changes to a brownish-red, whence it is concluded that either dichromic or chromic acid is in solution.

If a small quantity of acetone is added to the etherial solution of perchromic acid, the fluid may be heated gently to a temperature neighbouring on 50° C. The blue colour of the liquid gradually changes through grey to purple and to dark reddish-brown. This is, in all probability, dichromic acid, and its formation may be expressed thus:

(a) 4HCrO,→ 2H,CrO1, CrO, + 301⁄2. (B) 4H,CrO, + 702.

2H,CrO,,CrO, + 4H,0

What may be called the "conditions of preservation" of perchromic acid constitute important determining factors in connection with the decomposition of the compound. The conditions of preservation are: Low temperature and in a free state; ordi

nary temperature and in solution; ordinary temperature and free; elevated temperature and in solution, the solvent being ether.

Condition of Preservation.

Low temperature.
Free state.

Solid.

Ordinary temperature.

In solution.

Ordinary temperature.

Free state.

High temperature. In solution.

The general remark is: that perchromic acid, when in solution, owes its stability to the solvent; when free, to the temperature.

IV. ISOLATION.

The following remarks with regard to the crystallising of perchromic acid may be of interest.

Perchromic acid has been isolated; briefly the process is this:

Α solution of chromium trioxide in methyl ether at -30° C. is treated with 97 per cent. hydrogen peroxide solution. The blue crystals formed are said to be those of perchromic acid.

ORGANIC COMPOUNDS OF ARSENIC. PART II.

BY R. F. HUNTER, F.C.S.

In Part I. some account was given of atoxyl in general terms, and it is now proposed to treat the matter more thoroughly.

ATOXYL.

Owing to theoretical considerations current among the French school of chemists of Béchamp's time, Béchamp was prevented from arriving at the correct conclusion for his reaction, and further, the chemists of his day refused to regard his compound obtained from arsenic acid and aniline as a true organic arsenic compound, and, as stated in Part I., not until the work of Ehrlich, to whom we owe the discovery of our present most efficient cure for syphillus, appeared in the year 1907, was the true nature of Béchamp's compound demonstrated. Ehrlich and his co-worker Bertheim showed atoxyl to be

p. NH, CH. As O (OH),,

If, on the other hand, a frozen solution of potassium dichromate at -12° C. be treated with conveniently cooled and acidulated hydrogen peroxide, the superincumbent ether assumes a deep blue colour. The temperature being low, all remains solid, allowing the blue etherial solution to be poured off. At a temperature between -20° and -25° C. this liquid deposits blue crystals, which melt very rapidly when removed from the freezing bath.

This experiment was carried out by the writer previous to receiving information concerning the method by which perchromic acid was isolated in 1914.

and further, the commercial sodium compound to be

NH,CH,ASO (OH) O Na n H2O, where n varies between 2 and 6.

Researchers in this field following Ehrlich, applied the Béchamp reaction to other aromatic amines with a free para. position, this led to the discovery of 2-aminotolyl-5arsenic acid from o-toluidine.

As stated before, the main trouble involved in the use of atoxyl for injections is its toxic nature; acetylation in the case of such compounds as aniline had yielded the less toxic acetanilide. Consequently atoxyl was acetylated, and a drug of constitution, CH,CONHCH, As O (OH) O Na n H2O, was introduced.

It is necessary to examine systematically the derivatives of atoxyl, and I propose to again use Gibson's method of classification.

Gibson, in his recent work: Organic compounds of arsenic and antimony, has divided the atoxyl derivative as follows:

(1) p-Arsanilic acid and its N-Acyl and Alkyl derivatives. p-Arsanilic acid, Béchamp's compound, is usually prepared by

(3) Homologues and substitution products of p-Arsenilic acid homologues, such as Aminotolyarsenic acids, the 2-aminotolyl5-arsenic acid is important, and the sodium derivative NH, CH,(CH ̧) AsO (OH) O Na has found application under the title of "Kharsin."

o-Anisidine-4-arsenic acid is the most common derivative. 2: Acetyl 1:5 benzar

senic acid is an interesting example of an aminobenzarsenic acid.

The halogen derivatives are not important, the thio derivatives are classified under

and is prepared by diazotisation of both amino groups in benzidine or the sulphonic acid and coupling with 2-naphthylamine-3: 6-disulphonic acid.

(6) Organo mercurial compounds of pArsenilic acid and derivatives.

From the beneficial results of the use of mercury compounds in the treatment of venereal disease, we should expect a compound of the nature of p-arsenilic acid and mercury to be quite a good cure. Consequently it was attempted to combine the therapeutic properties of mercury with those of atoxyl, and the results were beneficial. Condensation of mercury acetate with atoxyl being main reaction, from which were obtained on successive concentration sodium 3:5-dehydroxymercuri-4-aminophenylarsinate.

A new compound tested clinically with poor results is "Hydryl," Hydryl," which has the composition,

(7) 4:4' Diaminodiaryl arsenic acids. These were discovered as a result of applying the Béchamp condensation to aniline and o-toluidine.

4:4 Diaminodiphenylarsenic acid. (NH, CH1), As O OH is the best example. (8) Mixed aromatic aliphatic p-amino arsenic acids.

(9) Nitro derivatives of arsenilic acids.
Some of these are important:
5-nitro-2-aminophenylarsenic acid.

6-Nitro-m-arsenilic acid.

2-nitro-4-aminophenylarsenic acid.
2-nitro-3-aminophenylarsenic acid.

3-nitro-4aminophenylarsenic acid are wor

thy of note.

(10 )Diaminophenylarsenic acids: Examples of these are: 2:3 diaminophenylarsenic acid, (NH2)2 CH, As O,H2.

3

3

HO (CO2H) CH, As O (OH)2, prepared from 2-acetylaminotolyl-5-arsenic acid by oxidation with KMnO, followed by NaOH hydrolysis. Its sodium salt is less toxic and is used sometimes in cases of syphillis.

2:4 Dehydroxyphenylarsenic acid. 2-Methoxy-4-hydroxyphenylarsenic acid. 2:4-dimethoxyphenylarsenic acid. 3:4-dehydroxyphenylarsenic acid and 4:4-dehydroxydiphenylarsenic acid have also been prepared.

(12) Nitro derivatives of hydroxyphenylarsenic acids.

3-nitro-4-hydroxyphenylarsenic

acid is

and

produced by nitration of sodium. p-Phenol arsenate with a mixture of HNO, H2SO, at 0° C., and has a structure,

is

HO (NO2) CH, As O (OH)2. 4-nitro-2-hydroxyphenylarsenic acid prepared from diazotisation of 4-nitro-2aminophenol, followed by warming to decompose diazo salt.

5-nitro-2-hydroxyphenylarsenic acid, 3:5dinitro-2-hydroxyphenylarsenic acid, and 5nitro-2:4-dehydroxyphenylarsenic acid have been prepared, and are worthy of mention. (13) Arsenic acids of amino phenols. amino-4-hydroxyphenylarsenic acid,

3

HỎ (NH,) C, H, As O (OH), is typical and is prepared by reduction of corresponding nitro compound.

3-amino-2-hydroxytolyl-5-arsenic acid, 4amino-3-hydroxyphenylarsenic acid, carbethoxy, 3-aminophenol-6-arsenic acid. 4-dimethyl amino-2-hydroxyphenylarsenic acid,

and

3:5-diamino-4-hydroxyphenylarsenic acid have been described and deserve mention.

PAN FORMATION IN SOILS IN THE LIGHT OF THE LIESEGANG PHENOMENON.

BY N. G. CHATTERJI, D.Sc., A.I.C.

The formation of pans in soils has been the subject of much investigation, and it may now be taken for granted that the whole process is intimately connected with the colloidal properties of soils. The latest work on the subject has been ably summarised by Morison (Trans. Farad. Soc., 1922, XVII., 2, 321-323), in which the author comes to the conclusion that the whole process is a transformation of soil colloids from the "sol" to the "gel" form with subsequent dehydration and deposition.

Whilst substantially agreeing with the above conclusion, an attempt has been made in the present paper to bring forward evidence showing the similarity between pan formation and that general type of periodic precipitation known as Liesegang phenomenon, after the name of the discoverer. This phenomenon was first observed by the discoverer when doing the following experiment:

A glass plate was coated with 5 per cent. gelatin solution containing a small amount of potassium chromate. A drop of strong silver nitrate solution was then placed on the gel, and it immediately began to diffuse into the latter. The silver nitrate, of course, reacted with the chromate in the gel, forming the insoluble red silver chromate. But although there was a continuous supply of both the components, the insoluble silver salt was, however, not deposited in a continuous zone round the periphery of the original drop, but in a series of concentric rings, separated by apparently

clear zones.

The general conditions observed with the soils ir which pans are formed are here given briefly, taken mainly from a paper on the subject by Morison and Sothers (Journ. Agri. Scien., 1914, VI., 84). The pan layer in a soil consists more or less of a weildefined band of material where the gradual transition from the surface to the underground soil is broken. The characteristics of this layer are a large diminution of pcre space of the soil cutting off the air and water movement and preventing the penetration of plant roots. The concentration of the soil into such a layer may be of two kinds : it may be caused by the continued passage of heavy instruments of tillage to a given depth, or by the removal of material either