PHASE RULE STUDIES ON THE PROTEIKS. III* BY WILDER D. BANCROFT AND C. E. BARNETT
Pentavalent Nitrogen in Organic Compounds. 11. In the preceding paper,' we discussed the conditions under which compounds containing one nitrogen atom in the molecule will or will not add hydrogen chloride stoichiometrically at ordinary temperature and under atmospheric pressure. I n this paper we propose to discuss the corresponding problem when there are two nitrogen atoms in the molecule. It will probably simplify matters if we repeat from the preceding paper the eight generalizations which constitute our working hypothesis. I. The tendency for a nitrogenous compound to react stoichiometrically with hydrogen chloride is increased when hydrogen is replaced by an alkyl group and is decreased when the hydrogen is replaced by a phenyl group, 11. Introduction of so-called negative radicals, such as 0, C1, Br, NOz, etc., decreases the tendency of the nitrogenous compounds to react stoichiometrically with hydrogen chloride. These radicals have most effect when attached directly to the nitrogen. 111. Carbonyl groups attached directly to the nitrogen or an aliphatic ethylene carbon linkage decreases the tendency of the nitrogen to react stoichiometrically with hydrogen chloride. For convenience of discussion we shall call two carbonyl groups attached to nitrogen a diketo linkage, a CO group and a C :C aliphatic group attached to nitrogen a keto-ethylene linkage, and two C:C aliphatic groups attached to nitrogen a di-ethylene linkage. Two keto linkages or one keto and one ethylene linkage will destroy the tendency to add hydrogen chloride unless compensated by the presence of alkyl groups, etc. Since there are not many data at best, we usually mean methyl or ethyl groups when we speak of alkyl groups. IT'. Two or more nitrogens attached to the same carbon atom destroy the tendency to combine stoichiometrically with hydrogen chloride for all but one of the nitrogens, except in so far as this may be compensated by the introduction of alkyl groups. V. I n general, linkage of nitrogen t o nitrogen seems to destroy the power of all but one of the nitrogens to combine stoichiometrically with hydrogen chloride, except in so far as this is compensated by the introduction of alkyl groups. VI. Hydrogen chloride does not add direct to nitrile nitrogen, an isonitrile nitrogen, or a cyanate nitrogen.
* Tlus work 1s part of the rogramme now being carried out at Cornell University under a grant from the Heckscher 8oundation for the Advancement of Research established by August Heckscher at Cornell University. 'Bancroft and Barnett: J. Phys. Chem., 34, 753 (1930).
WILDER D. BANCROFT AND C. E. BARNETT
1218
1’11. If the nitrogen is already pentavalent through formation of an intramolecular salt, hydrogen chloride can only be taken up stoichiometrically in case it displaces the other acid. VIII. Hydrogen chloride will add first to the nitrogen with which it will give the lowest dissociation pressure.
Substances containing Two Nitrogen Atoms It was mentioned in the preceding paper that in the ethylene amines the basicity is equal to the number of the nitrogens. The diamines add two molecules of hydrogen chloride, the triamines three, and the tetramines four.’ Diaminohexane adds two hydrogen chlorides. Lysine has two nitrogens and adds two hydrogen chlorides. Tryptophane has two nitrogens and must add two hydrogen chlorides unless it forms an intramolecular salt, in which case the ester must add two hydrogen chlorides. ‘so far, we have only found a record in the literature of a monochloride and nobody has studied the ester. In regard to the aromatic diamines, Sidgwick2 says:“The aromatic diamines are colourless, crystalline bodies which are much more soluble in water than the aniline bases. They form salts with two equivalents of acids. . . . The orthodiamines are remarkable for their great tendency to form ortho-condensation products; the two nitrogens joining up through the other body with which they react to form a new ring. Thus they combine with acids to form the anhydro-bases, cyclic amidines, or imidazoles:-
s””; KHz
p
+ HO\ PH3 =
N N
+
H20.
These bodies are strong bases and are thereby distinguished from the true amides, such as CsH,(NHCOCH3)2,which are formed with acids by the metaand para diamines. . . . “The ortho-diamines form similar ring compounds with nitrous acid, the
azimides:
\N
=
,^;>N
+
H20. These are
colourless, excessively stable substances, which can be boiled with alkali or heated to a high temperature without decomposition. They are thus sharpy1 distinguished from the diazo-compounds, and more particularly from the
2%
enormously explosive azoimide, HN-N, which contains the same chain of three nitrogen atoms. This difference also is no doubt due to the strain in the ring.” 2
Laubenheimer: “Die Grundzuge der organischen Chemie,” 298 (1884). Sidgwick: “The Organic Chemistry of Nitrogen,” 70 (1910).
PHASE RULE STUDIES ON THE PROTEINS
1219
The aromatic diamines combine stoichiometrically with two hydrogen chlorides, because the two nitrogens are not attached to the same carbon atom. I n the anhydro-bases the two nitrogens are attached to the same carbon atom and consequently these bases add only one hydrogen chloride. For the same reason the aliphatic and aromatic amidines’ only add one hydrogen chloride. “The [aliphatic] amides are strong, monacid bases, which form stable salts. The hydrschlorides generally crystallize well and are readily soluble in water and alcohol. The free amidines show an alkaline reaction, are very instable and decompose readily into ammonia and the corresponding acid.” “The phenyl amidines of the fatty acids are formed from aniline or the anilides by any one of a large number of reactions. One of the best is heating anilides with aniline hydrochloride.
CH,C(O).NH.C,Hs+CeH,NHz.HCl
CH,C( :N.C~HS)XH(HC~).CBHS
They are colorless compounds which crystallize readily. They dissolve in dilute acids to form salts. The salts contain one molecule hydrogen chloride per molecule amidine.” I n the three isomeric amido-benzylamines, C6H4(?;H2).CH~h”2,the two amino groups are not attached to the same carbon atom and consequently they add two hydrogen chlorides.2 “They are readily soluble in water, react alkaline, and take up carbon dioxide from the air. The primary hydrochlorides, C,He(NHz)*.HCl, react neutral, while the secondary hydrochlorides, C,He( ”2) 2.2HC1, redden litmus.” Sidgwicks says that diimine, CeH4(:NH)z, is “a colorless, crystalline substance. . . , It is not acidic, but weakly basic, forming a colourless hydrochloride.” It is easy to see why this compound should add one hydrogen chloride, but it is not clear why it should not add two. If one writes the formula with the two nitrogens connected, as we used to do in the case of quinone, the experimental result follows at once. Whether that is permissible is for the organic chemist to decide. Benzenyl amidine, C&.C( :NH)NH2, only adds one hydrogen chloride because the two nitrogens are attached to the same carbon. On the other C H :X /
/
hand glycyl glycine adds two hydrogen chlorides. Quinazoline, C6H4-N :CH, adds one hydrogen chloride because the two nitrogens are attached to the same carbon atom. On the other hand Hantzsch4 reports on a compound, C6HS\ C&OC&.C :N.C&.N:(CH~)Z. which is said to give one hydrochloride decomposed by water, whereas it should obviously take up two hydrogen chlorides. Meyer and Jacobson: “Handbuch der organiachen Chemie,” 1, 377 (1893);2, 193 (1902).
* Meyer and Jacobson: “Handbuch der organischen Chemie,” 2,243 (1902). a
“The Organic Chemistry of Nitrogen,” 73 (1910). Ber., 26, 926 (1923).
I220
WILDER D. BANCROFT AND C. E. BARNETT
Hydrazine adds two hydrogen chlorides. We do not have to predict this because hydrazine is not an organic compound. Substituting alkyl groups for the hydrogens should make the compound more strongly basic, while substituting a phenyl group should give a weaker base. This is exactly what happens. Ethyl and dimethyl hydrazines’ add two hydrogen chlorides, while phenyl hydrazine adds but one. Sidgwick2 says: “The primary alkyl hydrazines are very hygroscopic, strongly basic liquids. The secondary alkyl hydrazines, like the primary, are strongly basic, hygroscopic liquids, which are easily soluble in water. Mercuric oxide converts them into tetrazones, such as EtzN.N:N.KEt2,which are strongly basic liquids. . . “The primary and secondary aromatic hydrazines are decided mon-acid bases, forming salts with mineral and some organic acids. Unlike the primary fatty hydrazines they will not form salts with two equivalents of acid, but only with one. Secondary aromatic hydrazines: such as p2N.KHzwill form salts with one equivalent of acid, but these are partially decomposed by water. This is like the behaviour of the secondary aromatic amines, and is a sign of the negative character of the phenyl group. It is practically certain that it is only the NHz group which takes part in the formation of these salts. On the other hand the hydrogen of the K H group in phenyl hydrazine can be replaced by an alkali metal. . . . “Tetraphenyl hydrazine was first obtained‘ by the action of iodine on the sodium derivatives of the diphenylamine, p2r\r.Na;but it and its analogues can be prepared more simply5 by the oxidation of the diary1 amines with lead dioxide or potassium permanganate. “These bodies are remarkable for giving brilliant colours with mineral acids; in fact it is to the production of tetraphenyl hydrazine that the blue colour found in the diphenylamine test for nitric acid is due. These colours do not depend, as was a t first supposed, on the splitting of the molecule between the two nitrogens, since under proper conditions the hydrazine can be recovered unchanged. The coloured bodies are therefore coloured salts of the colourless hydrazines. Similar coloured compounds (not double salts) are formed by the addition of the halides of phosphorus, tin, iron, aluminum, and zinc. To account for this colour W-ielandO suggests that they contain a quinoid ring, and are in fact quinol derivatives: for example, the body obtained from tetra-tolyl hydrazine and hydrochloric acid may have the formula :c1 H C&GHa / )N.N:CeH,.CH3 CH3CsH4 I CsH4CH3
.
I
Meyer and Jacobson: “Lehrbuch der organischen Chemie,” 1, 249 (1893). “The Organic Chemlstry of Nltrogen,” 241,243,245 (1910). 8 [Sidgwick me8 (p to denote a phen 1 group]. * Chattaway and Engle,: J. Chem. 67, 10go (1895). Wieland and Gambarjan: Ber., 39, 1499 (1906). 6 Ber., 40,4260 (1907).
Jot.,
PHASE RULE STUDIES O N THE PROTEIXS
12-21
At first this seems impossible, since the quinols have no colour. But quinone diimine, Hlr::CGHI:SH is itself colourlese, while its derivatives of the type Ac I
hc I
(Alk)2: S :CsH, :X:(hlk)? in which the nitrogen has become pentad, and has no hydrogen attached to it, are brilliantly coloured; and we may well suppose that a similar change would produce a coloured compound from a colourless quinol.” Emil Fischerl found that with an excess of concent,rated hydrochloric acid ethyl hydrazine cryst,allized with two hydrogen chlorides. On recrystallization from water or on heating to IIO’, half the acid went off, leaving the compound C2HjNH.XH2.HCl. S o dissociation pressures were determined; but it is evident that there is quite a difference between the two and that the pressure-concentration curve would have two clearly-marked flats. Renouf2 prepared both hydrochlorides of dimethyl hydrazine. In the case of the unsymmetrical dimethyl hydrazine, the first hydrogen chloride must add to the more basic nitrogen, to the one to which the two methyls are attached, forming (CH2)&(HCl).XH2. While there is no direct proof of this, we can prove it indirectly by considering the addition of ethyl chloride to unsymmetrical phenyl ethyl hydrazine. We know3 that this forms C~H,(CZH,)Z.HC~.XHZ, because it gives diethyl aniline on reduction. The symmetrical dimethyl hydrazine4 also adds two hydrogen chlorides, obviously one t o each nitrogen. According to C u r t i u ~ benzyl ,~ hydrazine, C6HjCH21L”.?;H2, ad& on one hydrogen chloride. This must be pretty nearly a border line case. Asymmetrical monobenzoyl phenyl hydrazine adds one hydrogen chloride;e but is a weak base, the salt being decomposed partially by water. Nothing is said about any hydrochloride of dibenzoyl phenyl hydrazine. Tetraphenyl hydrazine’ is decomposed by dry hydrogen chloride dissolved in dry ether, so one cannot be sure whether the two form an instable stoichiometric compound or not. I t is of course possible that tetraphenyl hydrazine might be more stable in the presence of dry hydrogen chloride and in the absence of ether. Acetyl hydrazine undoubtedly adds hydrogen chloride. Michaelis and Schlundt* make no mention as to diacetyl hydrazine and hydrogen chloride, while Stolleg reports that both triacetyl hydrazine and tetrachloride hydrazine Ann., 199, 291 (1879). 13, 2171 (1880). a Meyer and Jacobson: “Handbuch der organischen Chemie,” 2, 320 (1902). ‘ Thiele: Ber., 42,2575 (1907). J. prakt. Chem., (2)62,95 (1899). Michaelis and Schmidt: Ber., 20, 43 (1887). Weland and Gambarjan: Ber., 39, 1501(1906). * Ber., 20,43 (1887);Widman: 26,945 (1893);27,2904 (1894);Hofmann and Marburg: Ann., 305, 220 (1899). J. prakt. Chem., (2) 69, 145 (1904). I
* Ber.,
’
.
WILDER D. BASCROFI’ AND C. E. BARNETT
1222
react acid and split off acetic acid. These compounds should be studied again to find just where the dividing line is and whether it could be moved one way or the other by introduction of a phenyl or a methyl group. Sidgwick‘ says that “the hydrazo compounds are neither basic nor acidic, the amino group being neutralized by the negative phenyl.” While we have not yet checked this, it cannot be right because azobenzene ad’ds on hydrogen chloride stoichiometrically and hydrazobenzene must be more basic because of the extra hydrogens. I n so far as hydrazobenzene might be converted into benzidine by hydrogen chloride, there would be some experimental difficulties; but we rather doubt their being serious. Of course hydrazobenzene is a symmetrical hydrazine and as such must add hydrogen chloride. Benzidine of course adds two hydrogen chlorides and so does benzidine
/CsH3-xH2 . Addition
sulphone,* SO2
of sulphonic acid groups decreases
\CGH3-”2 the strength of the base to such an extent that benzidine monosulphonic acid apparently adds only one hydrogen chloride, while the benzidine di-, tri-, and tetra-sulphonic acids apparently add none. One would rather like to see experiments made with hydrazo-triphenylmethane.3 [‘Hydrazo-triphenyl-methane, p3C.NH.HN.Cp3, like so many other compounds containing this radical, has a very peculiar behavior.‘ It is a comparatively stable substance, and is not oxidized at all by the air or by silver oxide. Stronger oxidizing agents, such as potassium permanganate or chromic acid, remove the hydrogen of the hydrazo groups; but the azocompound, p3C.N:N.Cp3,which we must suppose to be formed, breaks up a t once into nitrogen and triphenyl-methyl, p3C, which appears as its peroxide,
p&.o.o.cp~.
“Thus the relations which hold with the simplest aromatic derivatives (such as hydrazo-benzenef are here reversed. The hydrazo-compound is much more stable and the azo-body infinitely less so. Wieland expresses this by saying that the weak affinity of the triphenyl-methyl group makes the attachment of the hydrogen to the nitrogen in the hydrazo-compound much weaker than in hydrazo-benzene, while it is unable to hold the azo-group a t all.” It is rather curious about azobenzene. It was believed by van’t Hoff that azobenzene did not add hydrogen chloride at all. Meyer and Jacobson6 say that “azobenzene combines with benzene, bromine, hydrogen chloride, and hydrogen bromide to form addition compounds which decompose readily.” On the other hand, Rosecoe and Schorlemmer6 give a good deal of interesting detail. “The Organic Chemistry of Nitrogen,” 254 (1910). Griess and Duisberg: Ber., 22, 2459 (1889). 3 Sidgwick: “The Organic Chemistry of Nitrogen,” 255 (1910). Wieland: Ber., 42, 1902 (1909). 5 “Handbuch der organischen Chemie,” 2, 2j6 (1902). 6 “A Treatise on Chemistry,” 3 111, 291 (1887). 1
PHASE RGLE STUDIES O S THE PROTEINS
1223
"Azobenzene crystallizes from alcohol or petroleuin spirit in yellowishred plates which melt at 68" and have faint odour of roses. I t boils at 293' and its vapour has a sp.gr. of 6 . 5 . On the spontaneous evaporation of its solution in benzene, the compound ClrHloK? CCHs separates out in long, thick, yellowish-red prisms which effloresce in the air. If hydrochloric acid gas be passed into a solution of azobenzene in carbon disulphide, a yellow crystalline compound, (CI2Hlo?U'?),.3HCl,is formed; the analogous hydro-
+
,so
100
200
'I'D
FIG.I
bromic acid compound is a carmine-red crystalline mass. Bromine, added gradually to a solution of azobenzenc in chloroform, forms the addition product, Ci2H10S?.Br6, which separates in largc dark-red prisms. A11 these compounds decompose in the air leaving a residur of azobenzene." Our generalizations lead to the assumption that azobenzene should takc up one hydrogen chloride but did not call for more. C'onsrquently, we checked up to see whether Roscoe and Schorlrninirr were right. They were, as Fig. I shows. I t was a simple matter to find a way out of the difficulty. Our generalizations call for the addition of two hydrogen chlorides and not three to the nitrogens in t'wo azobenzenes; but \w arc dealing only with direct addition of hydrogen chloride t o nitrogen. If \wwrit? the formula,
FI C'eH:,.StH('I):S.(',Hs
I
('eHa.S(HC'1)
:k.C'&> ('1
the third hydrogen chloride does not add direct to nitrogcn and we are no more concerned with it than we arp with the addition of hydrogen chloridp to hydrogen cyanide to form HC(C'1j : S H . X
