NOTES
March, 1949 When mercury(1) nitrate was added t o a dilute solution of orthophosphoric acid, a pure white crystalline precipitate was obtained which did not change color. The precipitate was filtered, washed with water and dried in a desiccator over anhydrous calcium chloride. Anal. Calcd. for Hg,HP04: Hg, 80.71. Found: Hn, 79.2, 80.8. The various concentrations of phosphoric acid were made by diluting a stock solution whkh had been prepared from 85% acid and standardized by titration against standard sodium hydroxide using thymolphthalein as indicator. The platinized platinum electrodes were prepared with the usual care. Several were used and they checked with each other to within 0.3 millivolt. The hydrogen was bubbled through a solution of chromous chloride acidified with acetic acid4 t o remove oxygen, then through a solution of phosphoric acid of the same concentration as that used in the cell. The cell was H-shaped with a sintered glass diaphragm in the horizontal arm. Potentials were meatured with a Rubicon, type B, potentiometer a t 25 * 0.05
.
1115
TABLE I OF CELLSAND CALCULATION OF STANDARD POTENTIAL POTENTIAL, Eo,OF THE CELL m
E
0.001026 .01026 .02052 .05130 .I032 .2071
0.7998 .7730 .7601 .7433 .7341 .7215
E
aHaPO4
0.7995 .7750 .7600 .7453 .7336 .7221
0.0001050 ,004204 .01223 .03440 .08057 .1776
L
0.6191 ,6409 .6406 .6382 .6388 .6368
TABLE I1 STANDARD POTENTIAL CALCULATED FROM DEGREEOF IONIZATION DATA m
a
0.01026 .02052 .05130 ,1032
0.599 .492 .366 .290
E 0.7740 .7600 .7443 .7339
Eo'
Eo
0.6432 .6421 .6423 .6438
0.6400 .6378 .6365 .6365
The cells made with the yellow tertiary mercurous phosphate did not give constant or reproducible potentials. In all cases the potential DEPARTMENT would decrease with time and approach a mini- CHEMISTRY UNIVERSITY mum value. I n some cases the yellow phosphate PURDUE LAFAYETTE, INDIANA RECEIVED JULY 26, 1948 had changed to a white color in the 0.2 M phosphoric acid after several days. Typical potentials were 0.7364, 0.7392 and 0.7492 decreasing t o The Ziegler Bromination of Ethyl Tetrolate 0.7245, 0.7228 and 0.7313 after seven days. The cells made with the white secondary BY J. ENGLISH, JR., AND J. DELAFIELD GREGORY~ mercurous phosphate gave fairly constant and I n a recent review article Djerassi2 commented reproducible results and equilibrium values were on the lack of data on the reactions of N-bromoestablished within one day. For the cell Hz (a = 1)) H3POd(m), HgzHPOd(s), Hg, the cell reaction succinimide with acetylenic compounds. This HgZHP04 = H + HzP04Hg, and prompts us to record our observations on the is H2 if the secondary and tertiary ionizations are bromination ofethyl tetrolate by this method. Tetrolic acid was synthesized by the action of assumed to be negligible, the potential a t 25' is given by the equation E = Eo-0.02957 log carbon dioxide on propynylmagnesium bromide U H + ~ H ~ P O , - . For a H + a H 2 P 0 , = K I ~ H ~ P the O ~ , and converted to its ethyl ester in the usual value of k'l = 7.516 X IO-3 was used as reported manner.3 Pure samples of the ester were then by NimsJ The activities of the undissociated dissolved in carbon tetrachloride and treated phosphoric acid were taken from the results of with N-bromosuccinimide a t reflux temperatures, Mason and Blum.6 The calculated molal stand- with addition of benzoyl peroxide, under ultraard potential of the cell is given in the last column violet light, without either, and finally in a sealed of Table I. The Eo for the most dilute solution vessel a t 150'. I n all cases most of the ester does not agree with the other values. Excluding was recovered unchanged. The only product that could be isolated in pure form was ethyl that value, the average is 0.639*0.002 volt. An independent calculation for the Eo of the a,P-dibromocrotonate, resulting apparently from cell can be made by using the Debye-Hiickel the addition of two atoms of bromine a t the triple limiting law for the mean ion activity coefficient bond. A somewhat analogous addition reaction acof phosphoric acid and by using the degree of companying the Ziegler bromination of cyclodissociation, a, tabulated by Mason and Blum,6 to calculate the concentration, ml, of the hydrogen butene and methylene cyclobutane has been In the and the dihydrogen phosphate ion. The previous reported by Buchman and H ~ w t o n . ~ 0.05914 log am = present instance, although no hydrogen bromide equation becomes Eo' = E was noted, the rather extensive decomposition Eo 0.0301~'ZZ, using log y* = -0.5085+ and ,u = ml = am. The results of such a cal- observed might well have produced some of this culation are given in Table 11. The average substance and hence made bromine available to value of 0.638 * 0.002 for the Eo of the cell the reaction mixture as pointed out by these agrees better than one should expect. The authors. (1) Present address: Rockefeller Institute for Medical Research, molal potential for the electrode Hg, Hg2HP04, N. Y. HzP04-is -0.639 * 0.002 volt a t 25'.
+
+
+
+
+
(2) C. Djerassi, Chem. Rev., 43, 296 (1948); see also
(4) Stone and Skavinski, 2nd. Eng. Chcm., Anal. Ed., 17, 495 (1946). (5) Nims, TEXIS JOURNAL, 66, 1110 (1934). (6) Mason and Blum, ibid., 69, 1246 (1947).
K.Jachinowski,
A.
Wohl and
Bcr., 64, 476 (1921). (3) Stols, communication cited in Beilstein, 11, p. 480. (4) E. R. Buchman and D. R. Howton, THIS JOURNAL, 70, 2517, 3510 (1948).
NOTES
1116 Experimental
A suspension of 19.5 g. of N-bromosuccinimide in 30 cc. of carbon tetrachloride was mixed with 12.0 g. of ethyl tetrolate and 0.5 g. of freshly recrystallized dibenzoyl peroxide. After fiftv minutes a t reflux temDerature the Dale yellow solution was decanted from 15-g. of dark tarry material, the solvent evaporated and the residue distilled. In addition to 6.6 g. (55%) of ethyl tetrolate there was obtained 3.5 g. (1277”) of a fraction boiling a t 68-75’ a t 2 mm. This product was combined with those from other experiments and carefully fractionated t o yield pure ethyl a,fl-dibromocrotonate b. p. 58.5-60’ a t 0.8 mm., n z o D 1.5175, d*od 1.744. Anal. Calcd. for CeHsOzBrz:C, 26.50; H , 2.96; Br, 58.77. Found: C, 26.60; H, 3.05; Br, 58.62. For further identification a sample was saponified by refluxing with 10% aqueous potassium hydroxide. From the highly colored product there was isolated by extraction with ligroin pure a,b-dibromocrotonic acid, m. p. 118.5-119.5’. Michael reported the melting point of this substance as 120O.6
Vol. 71
It thus seems probable that the addition of bromine to the double bond is followed by the loss of hydrogen bromide, forming 2t-methy1-3~,5t-dinitro-a-bromochalcone (IV). Experimental
2-Methyl-3,5-dinitroacetophenone.-2-Methyl-3,5-di-
nitrobenzoyl chloride was prepared by heating a mixture of 45 g. of 3,5-dinitro-o-toluic acid,’ 35 ml. of purified thionyl chloride, and 200 ml. of dry benzene under reflux until the acid completely dissolved. The solvents were then removed by distillation under diminished pressure, and the residue was dissolved in 250 ml. of dry ether. This ether solution was used without further purification, An ether solution of the ethoxymagnesium salt* of malonic ester was made in the following manner: Five milliliters of absolute ethanol, 0.5 rnl. of carbon tetrachloride, and 5.25 g. of magnesium turnings were placed in a flask and allowed to react for a few minutes. Seventyfive milliliters of anhydrous ether was then added and t o this mixture a solution of 35.2 g. of ethyl malonate, 20 ml. of absolute ethanol and 25 ml. of dry ether was added ( 5 ) A. Michael, Bcr., 84,4221 (1901). a t a rate such that mild refluxing was maintained. STERLING CHEMISTRY LAB. When the magnesium had dissolved, the solution of 2YALEUNIVERSITY methyl-3,5dinitrobenzoyl chloride was added with stirRECEIVED NOVEMBER 17, 1948 ring over a period of thirty minutes. The contents of the NEWHAVEN,CONN. flask were then heated under reflux for an additional thirty minutes and then acidified with dilute sulfuric acid. The ether layer and an ether extract of the water layer The Condensation of 2’-Methyl-J’,5’-dinitro- were combined and the solvent was removed by distillachalcone with Ethyl Malonate tion. The residual liquid was heated under reflux for four hours in a mixture of 60 ml. of acetic acid, 7.5 ml. of BY REYNOLD C. FUSON AND GEORGE MUNN concentrated sulfuric acid and 40 ml. of water. The mix2’-Methyl-3’,5’-dinitrochalcone(I) was pre- ture was cooled, diluted with water and extracted with ether. The ether was washed with sodium bicarbonate pared in the hope that it might undergo an intra- solution, dried over calcium chloride, and the solvent was molecular Michael condensation to yield the Cor- removed by distillation. The residue was distilled under responding substituted a-tetralone. However, diminished pressure a t 150-152 O (2 mm.) The yield was under the conditions ordinarily employed for 27 g. (60%). When recrystallized from methano!, the melted a t 72-73 Michael condensations no ring closure occurred. 2-methyl-3,5-dinitroacetophenone Anal. Calcd. for C ~ H ~ N ~ O C,S 48.24; : H, 3.60; N, T h a t this chalcone is capable of undergoing reac- 12.50, Found: c, 48.47; H, 3.79; N, 12.40. tions of the Michael type was demonstrated by con2 t-Methy1-j ’,5’-gmitrochalcone (1).-Dry hydrogen densing i t intermolecularly with ethyl malonate. chloride was bubbled slowly over a period of two days into The product (11) which was obtained when the a solution of 22.6 g. of 2-methyl-3,5-dinitroacetophenone 12 ml. of benzaldehyde in 150 ml. of glacial acetic acid. chalcone was allowed to reactwith ethyl malonate and During this time a crystalline precipitate appeared. The was and the acid mixture was then heated under reflux for two hours and boxylated to form 2-phenyl-3-(2-methyl-3,5-dipoured on ice. The white precipitate which formed was collected on a filter and recrystallized from ethanol. nitrobenzoy1)-butyric acid (111). Twenty-one grams of 2’-methyl-3’,5’dinitrochalcone was obtained; m. p . 128-129’; 67%. Anal. Calcd. for C l a H 1 ~ N ~ O C, ~: C H ( C O ~ C ~ H ~61.53; )~ H, 3.88; Found: C, 61.65; CsHnN H , 3.90. N0z NOz Condensation of 2 ’-Methyl3 ’,5’-diI I1 nitrochalcone with Ethyl Malonate.-A mixture of 3.1 g. of 2‘-methy13’,5’-di, JBrz &HpO nitrochalcone, 2 ml. of ethyl malonate, 100 ml. of absolute ethanol, and 5 drops of piperidine was heated under reflux for OnN/ CoCHrCHCHzCozH twenty-four hours. It was then diluted with water, acidified and extracted with &Ha ether. The ether layer was dried over calcium chloride, and the solvent was NOz N0z removed by distillation. The residue IV I11 was recrvstallized several times from The 2‘-methyl-3’,5’-dinitrochalconeyielded a methanol with the use of charcotl; 1.8g. of white crystals was Obtained; m *p‘ 96-97 . monobromo derivative when i t was allowed to re- (Ir) Anal. Calcd. for C23HZ4N20g:C, 58.47; H , 6.12; act with bromine in acetic acid solution. Oxida- N,. 5.93. Found: c, 58.78; H, 5.16; N, 6.09.
.
.
6
tion of the bromochalcone with permanganate produced 3,5-dinitro-o-toluic acid, showing that the bromine was not attached t o the methyl group.
(1) McGookin, Swift and Tittensor, J. SOC.Chem. I n d . ( T r a n s . ) . 08, g2 (1g40). (2) w d k m and Hauser, THISJOUENAL. 68, 1386 (1946).
