T H E CATALYTIC PREPARATION O F 24-DIXi\lINOPHENOL* BY K. E . BRADT**
Introduction Hemitian,’ Gauhe,2 PomeranzI3and Stuckenburg4 have described methods for the chemical reduction of 2-4-dinitrophenol to 2-4-diaminophenol. Reducing agents used were PI3 with water, and hydrochloric acid with zinc, tin, or iron. a-4-Diaminophenol has been prepared by electrolytic methods from m-dinitrobenzene5 and from 2-4-dinitropheno16 . The authors have obtained a material yield of 94.4 percent of 2-4-diaminophenol by the electrolytic reduction of 2-4-dinitrophenol in sulphuric acid solution. Apparatus The apparatus consisted of a steel autoclave connected to a commercial hydrogen cylinder. It has been described by 0. W. Brown, G. Etzel and C . 0. Henke.’ Materials The a-4-dinitrophenol was prepared from I-chlor-2-4-dinitrobenzeneby refluxing with aqueous sodium carbonate. The sodium salt was then steam distilled t o remove any unchanged chlor compound. Acidification with sulphuric acid precipitated the phenol, which mas mashed free from sulphates, then dried. It melted at 113’ C. Absolute ethyl alcohol, which was used as solvent, was prepared by digestion, first over freshly reburned CaO, then over KOH, and finally was distilled through an eight inch Hempcl still-head. I t boiled a t 78-79’ C. (corr.). The catalyst was prepared by reducing S i c 0 3 (Baker’s Analyzed) in a Pyrex combustion tube by a current of commercial electrolytic hydrogen at 288’ C. The hydrogen was passed over the carbonate at a rate of 31 liters per hour until the reduction was complete. The rate was then reduced to six liters per hour until the apparatus had completely cooled. The furnace used has been de.cribed in detail by Brown and Ilenke.a * This paper is constructed from work done a t the suggestion of and under thedirection of 0. W. Brown, Professor of Chemistry, Indiana University. * * Assistant Professor of Chemistry, The State College of Washington, Pullman, Washington. ’Ber., 8, 768 (187j). Ann., 147, 66 (1868). 3 D. R. P. 269, j42. Ber., 7 , 1322 (1874); 10, 38 (1877); A4nn.,205, 66 (1880). 5 Ber., 26, 1848 (1893). 6 Elbs: 6. prakt. Chern., (2) 43, 39 (1891);Weyprecht: Brockman’s “Electro-Organic Chemistrv,” 2;j-6 (1926); Brand: Ber., 38, 4006 (190j); Hofer and ,Jakob: 41, 3187 (1908); Bradt ana Brown: Trans. Am. Electrochem. Soc., 315-328 (1929). J. Phys. Chem., 32, 631-635 (1928). h J. Phgs. Chem., 26, 163 (1922).
W . E. BRADT
2712
Procedure Accurately weighed amounts of P-4-dinitrophenol and catalyst, with 20 ml. of solvent, were placed in the autoclave. h slow current of hydrogen was passed through the pipes while the autoclave basin was being bolted into position. A lead gasket was used to prevent leakage. Hydrogen pressure was applied from a large tank until the pressure in both the autoclave and a small tank was exactly equal to that desired. The small tank acted as a reservoir to prevent variation of pressure during the reduction period. The external resistance was adjusted to obtain the desired temperature and this temperature was maintained with a maximum variation of two degrees. 95
FIG.I
The Effect of Reduction Temperature
After reaching the desired constant temperature, the apparatus was shaken by the eccentric at about 175 r.p.m. during the reduction period, usually two hours. After opening the apparatus, the reaction products were washed into a beaker containing 50 ml. of concentrated HC1. This solution was then diluted to one liter and the amine estimated by titration against a standard solution of sodium nitrite. CeH30H(NH*)Z 2HC1 2HONO = C ~ H B O H . ( N N C ~ )4H20 ~ Experimental Results The effect of the variation of temperature is shown by data in Table I and Fig. I . It will be seen that at 96' C. a maximum yield of 91 percent is obtained. At 90' C. great variations in the yield of diamine occur. Above 96' C. the decrease in yield is accompanied by an increasing formation of ammonia. At 125' C. the odor of ammonia in the product is very strong.
+
+
+
CATALYTIC PREPARATIOK O F
2-4-DIAMISOPHEXOL
2713
TABLE I Effect of Reduction Temperature Compound = 5 .o gm. 2-4-dinitropheno1, precipitated, washed and dried. Solvent = 2 0 . ml. absolute ethyl alcohol, refluxed over CaO. Catalyst = 1.0 gm. Ni reduced at 288'C. from S i C 0 3 . Pressure = 500 lbs. hydrogen per sq. in. Agitation = I 7 5 r.p.m. Time = 2 . 0 hours. Reduction temperatures in "C.
Yield in % of theory
90 90
56 . o
90 90
79 . o 89 . o
93 93
89.2
59 . o
90.6
Av. Yield in % of theory
70.8
89.9
96
90.5
96
91.5
96
93.2
96
94.7
I02
86.2
I02
85.4
85.8
125
80.;
80.j
I 2j 1 2 j
92.5
77 .5 83.4
Variations in yield caused much difficulty throughout this investigation. Efforts to control conditions were successful only when all the materials used had been protected from the fumes of the laboratory. hlethods of purification of dinitrophenol which necessitated contact with laboratory fumes invariably caused decreased yields of diamine. The effect of the length of the reduction period was studied, using dinitrophenol which had been crystallized once from commercial 96y0 alcohol. The reduction period was varied from 40 minutes to four hours. Since only a slight increase was observed above two hours, the time of reduction was maintained at that value. These data are presented in Table I1 and Fig. 2 .
2714
TV.
E. BRADT
The effect of the concentration of 2-4-dinitrophenol was studied, first, with the ratio of the grams of catalyst to the grams of dinitrophenol, equal to one-fifth, and again, with this ratio equal to two-fifths. Very little decrease in yield resulted from an increased concentration of dinitrophenol. These data are presented in Table 111. A consideration of Table I11 will show a slight increase in yield, due to the use of the larger amount of catalyst. This
1 2 TIE3 LY HOURS
0
3
4
FIG.2 Effect of Reduction Time
TABLE I1 Effect of Reduction Time Compound = 10.0gm. 2-4-dinitrophenol, crystd. from comml. 96% alcohol. Solvent = 20.0 ml. absolute ethyl alcohol, refluxed over CaO and KOH. Catalyst = 1.0gm. Xi reduced at 280' C. from SiCOs. Temperature = 96OC. Pressure = 500 lbs. hydrogen per sq. in. Agitation = 1 7 5 r.p.m. Yield in 70 of diamine
Av. Yield in %o of theory
40.9 44.0
42.5
0.66 .o .o
43.7 44.3
44
1.j
63.3
63.3
Reduction time in hrs.
0.66
I I
0
Reduction time in hrs.
Yield in "c of diamine
Av. Yield in % of theory
2
.o
.o
81.5 81.5
81.5
2
3 .o 3 .o
83.2
83.4,
83 .j
4.0
4.O
85 . o 85.2
85.I
2715
CATALYTIC PREPARATION OF 2-4-DIAMISOPHENOL
apparently exerts a considerable effect at low concentrations of dinitrophenol, possibly because a smaller amount of catalyst was completely "poisoned" by substances in the solvent. There appears to be an optimum concentration of 2-4-dinitrophenol above and below which the yield of the diamine decreases. With a ratio (catalyst to compound) of one-fifth, this is five grams 2-4-dinitrophenol in 20 ml. of solvent. When the catalyst to compound ratio equals two-fifths the optimum concentration of 2-4-dinitrophenol is two and one-half grams per 2 0 ml. of solvent. TABLE I11 Effect of Concentration of Dinitrophenol Compound = ~-4-dinitropheno1,precipitated, washed and dried. Solvent = 20.0 ml. absolute ethyl alcohol, refluxed over CaO and KOH Catalyst = 1.0 gm. Ni reduced at 288' C. from NiCOs Temperature = 96' C. Pressure = joo lbs. hydrogen per sq. in. Agitation = 175 r.p.m. Time = 2.0 hrs. Grams of dinitrophenol
Ratio of Catalyst to dinitrophenol
% Yield of diarnmophenol
Av. Yield in R of theory
50 .o
53.5
57.0 91.5 91.5
91.5
90.8 90.8
90.8
87.7 87.6
87.7
87.6 87 . o
87.3
89.2 89.7
89.5
94.9 95.1
95 . o
91.5 92 0
91.8
90.5 90.4
88 . o 92 . o
90.0
2716
W. E. BRADT
The effect of the solvent on the reduction of a-+dinitrophenol is shown by data presented in Table IV. It will be noted that the highest yields were obtained by using absolute alcohol as a solvent. The apparent impurity of some of these solvents is partially refuted by the fact that reduction of p-nitrophenol to p-aminophenol occurs in good yield in each one. These data are included in Table IV. TABLE IV Effect of Solvent Compound = 5.0 gms. a-+dinitrophenol, precipitated, washed, and dried. Catalyst = 1.0 gm. Ni reduced at 288' C. from NiCOI. Temperature = 96' C. Pressure = joo lbs. hydrogen per sq. in. Agitation = 1 7 5 r.p.m. Time = 2.0 hrs. Solvent
Benzene (thiophene free) Toluene (thiophene free) Xylene (thiophene free) CHIOH (absolute) Acetone (U.S.P.) Water (distilled) Alcohol (comml.) Alcohol (absolute) Alcohol (dehydrated over CuSOa)
Yield of Barnnophenol 23
.o
20.0
00.0
7 7 .o 89 .o 00.0
57 .o 91.5 94.7
Compound = 10.0 gms. p-nitrophenol, recryst., m.p. = 114' C. Temperature = 1 2 5 ' C. Other conditions = as above. 70 Yield of Solvent
Benzene (thiophene free) Toluene (thiophene free) Xylene (thiophene free) CH,OH (absolute) CHIOH (absolute) Acetone (U.S.P.) Water (distilled) Water (temp. 148' C.) Alcohol (comml.) Alcohol (absolute)
p-aminophenol 100.0 100.0
100.0
93 5 95.6 87 . o 91.2 99.2 '
88.0 100.0
Increasing the hydrogen pressure to 1000 lbs. per square inch failed to increase the yield of diamine. Evaporation of the reduction products in an atmosphere of hydrogen yielded a black gum which in one case contained 59% of diamine. However, pouring the contents of the autoclave into concentrated aqueous HCl caused
CATALYTIC PREPARATIOS- O F 2-4-DIAMISOPHESiOL
2717
the formation of a light pink non-crystalline solid which rapidly became brown. A reduction which had yielded 93.270 diamine was duplicated; the contents of the autoclave were precipitated in this manner and filtered; the residue was washed twice with concentrated aqueous hydrochloric acid to remove any nickel salts, evacuated over P205 and solid XaOH for 24 hours, weighed and titrated against standard sodium nitrite solution. Xine and one-half grams of goy0 pure 2-4-diaminophenol hydrochloride were isolated. This represented 5 0 . 6 7 ~recovery of the theoretical amount of diamine. The product was also isolated by pouring it into anhydrous alcoholic HC1. After filtration and desiccation, analysis indicated the recovery of 50ycof the theoretical diamine as the 76% pure hydrochloride. KO dinitrophenol was observed. The same product was prepared according to the method of Stuckenberg. When one hundred grams of 2-4-dinitrophenol were reduced by zinc dust and concentrated HC1, only thirty per cent of the theoretical diamine was recovered as the 9076 pure pink crystals of hydrochloride. The 2-4-diaminophenol hydrochloride is soluble in cold water, insoluble in concentrated hydrochloric acid, alcohol, ether, and acetone.
Summary An absolute alcohol solution of 2-4-dinitrophenol was reduced to 2-4-diaminophenol in the presence of a nickel catalyst under joo lbs. of hydrogen pressure. I.
RIaximum yields of diamine were obtained at a temperature of 96' C. 2. Higher temperatures caused a slight decrease in the yield of amine, with the formation of ammonia a t 125' C. 3 . Increase of the time of reduction beyond two hours caused only a slight increase in the yield of diamine. 4. Variation of the concentration of 2-4-dinitrophenol (when the ratio of the grams of catalyst to the grams of dinitrophenol equalled one-fifth) caused a maximum yield of 91.jc: at a concentration of j.0 grams in 2 0 . 0 ml. of solvent.
5 . When the ratio of the grams of catalyst to the grams of z-4-dinitrophenol equalled two-fifths, variation of the concentration ofthe dinitrophenol gave a maximum yield of 95.1% diamine from 2.5 grams in 2 0 ml. of solvent. 6 . Increasing the value of the ratio, of the grams of catalyst to the grams of dinitrophenol, from one-fifth to two-fifths caused an increase in the yield of diamine a t all concentrations investigated. Absolute ethyl alcohol dehydrated at room temperature over anj. hydrous copper sulphate gave higher yields of diamine than other solvents investigated. 8. Fifty-nine per cent of the theoretical diamine was isolated as free amine in the form of a black gum. Fifty per cent was isolated as the eighty
2718
W. E. BRADT
per cent pure diamine hydrochloride, C6H30H(NH~)~-zHC1.Only thirty per cent was isolated as the 90% pure diamine hydrochloride when the reduction was performed with Sn and HC1. 9. A maximum yield of 95.1% of 2-4-diaminophenol was obtained by the following conditions: Compound = 5.0 gm. z-4-dinitrophenolJ precipitated, washed, and dried, Solvent = 20 ml. absolute ethyl alcohol dehydrated a t room temperature over CuSO,. Catalyst = 2 . 0 gm. nickel reduced from NiCOsJ a t 288' C. Temperature = 96' C'. Pressure = joo lbs. comml. electrolytic hydrogen per sq. in. -4gitation = 17s r.p.m. for two hours.
