S CH3 sulfur, and dimethyl
formamide
^ \
2-Methylbenzo-C—C—NH—CH3 thiazole, sulfur, and 116 119°
g / y methylformamide
Nv \ /C Hs
2-Methylbenzo-C - 2-Methylbenzo-C — N thiazole, sulfur, and 103-105°
\ ? H3 dimethylformamide
2,5-Dimethyl-N 2,5-Dimethyl-N pyrazine, sulfur, and
methylformamide S = C — NH-CH3
/CH3
S=C—N^
) \C H3
2,5-Dimethyl-N 2,5-Dimethyl-N pyrazine, sulfur, and 283-285°
^ ( CH3 dimethylformamide
44 R. WEGLER, E. KUHLE, AND WERNER SCHAFER
tants are heated to 315° before the xylene is mixed with the solution by agitating the glass tube; the pressure then rises to about 135 atm. Heat
ing is continued for a further 90 min; on cooling, the gases formed (20 gm H2S) are released. Volatile material is removed from the liquid product by steam distillation at pH 6, and sulfur removed from the residue by filtration. The filtrate is heated with sodium hydroxide (60 gm), acidified to pH 6, treated with activated charcoal, and filtered. The filtrate is acidified to pH 2 with hydrochloric acid, and the isophthalic acid (90.5 mole % ) filtered.
Example 31: Oxidation of mercaptans with sulfur (110). 2-Phenyl-ethyl mercaptan (1 part) and ammonium polysulfide solution (5 parts) are heated in an autoclave for 4 hr at 205°. Phenylacetamide is formed in 95% yield. It is isolated by evaporating the reaction solution to dry
ness, extraction with hot alcohol, and recrystallization from the same solvent; m.p. 153-154°.
Similarly, if n-decyl mercaptan (1 mole) is heated with sulfur (2 moles) and aqueous ammonia (28%, 5 moles) for 12 hr at 200°, an almost quantitative conversion into n-nonanecarboxylic acid amide, m.p.
97-98°, takes place.
The corresponding alcohols only afford yields of 40-50% of the acid amides; nor do the yields obtained from secondary mercaptans quite compare with those from the primary compounds.
Example 31a: Conversion of vinylpyrrolidone into N-thioacetyl-pyrrolidone (111b). N-VinylN-thioacetyl-pyrrolidone (100 parts) is heated, with stirring or shaking, with sulfur (85 parts) and hydroquinone (2 parts) for 6-8 hr at 160-170°. The dark-colored reaction product is dissolved in tetrahydrofuran, treated with animal charcoal, filtered, and concen
trated. A dark, noncrystalline substance (180 parts) of composition C8H9ONS is obtained, and can be shown to be the dimer of N-thioacetyl-pyrrolidone by molecular weight determination. The compound is com
pletely soluble in water and melts in the range 48-93°. Boiling with dilute sulfuric acid and methanolic hydrochloric acid (20%) causes the elimination of H2S. The substance is completely hydrolyzed after 8 hr, yielding acetic acid and y-hydroxybutyric acid.
Example 32: N,N'-Dicyclohexyldithiooxalic acid diamide from acet
ylene (113). Cyclohexylamine (198 gm) is placed in a four-necked flask fitted with a stirrer, thermometer, reflux condenser, and gas inlet, and acetylene passed in until the saturation point is reached. Sulfur (106 gm) and dioxane (150 ml) are then added and the mixture heated to boiling. Acetylene is slowly passed for 3 hr, and heating continued for a further 2 hr. The dioxane is evaporated under vacuum, and the semisolid residue extracted with boiling alcohol (500 ml) and filtered. The solid
THE REACTIONS OF SULFUR 45 filtration residue is placed in boiling butanol (250 ml) and filtered hot.
On cooling, N,N'-dicyclohexyldithio6xalic acid diamide (11 gm) m.p.
156-158° separates from the filtrate.
Example 33: Nonane-1,9-dicarboxylic acid from undecylenic acid (23). Purified undecylenic acid (3.68 gm) is heated with an oxidizing solution for 4 hr at 160°. The reaction product is saponified by alkali, and acidification yields nonane-1,9-dicarboxylic acid. Recrystallization from chloroform affords the pure acid (1.52 gm, 35%), m.p. 111-112.5°.
The oxidizing solution is prepared as follows: For every 0.1 mole of the compound to be oxidized, 7 N ammonium sulfide solution (7iV with respect to the sulfide and 12N with respect to the ammonia) (25 ml), sulfur (0.5-1 gm atom) and pyridine or dioxane (12-25 ml) are used.
Ammonium thiosulfate (0.1 mole) is also added.
Example 34: Preparation of a trithione from isobutylene and sul
fur/sulfur dioxide (52). Isobutylene (170 gm), sulfur dioxide (213 gm), and sulfur (192 gm) are heated in a high-grade steel autoclave of 1600 ml capacity for 2 hr at 180-195°. A dark oil (426 gm) and an aqueous liquid (131 gm) are obtained. The oily product is distilled at 118-122°/1 mm, yielding C4H,S3 (186 gm), m.p. 37-38.3°.
Example 35: 4,4'-&tilbenedicarboxylic acid from p-toluic acid and sulfur (109). A mixture of p-toluic acid, at least 97% pure, (1 mole) and sulfur (0.5 mole)—up to 1 mole of sulfur can be used—is heated in a three-necked flask for 41/2 hr at 270-275°. A yellow precipitate of 4,4'-stilbenedicarboxylic acid gradually separates from the ever-darkening reaction liquid. When the evolution of H2S has ceased, the mixture is cooled to 140° and hot xylene (5 ml/gm of p-toluic acid) added. The mixture is again heated under reflux for 30 min, filtered hot, and the filtration residue washed with hot xylene. After evaporation of the xylene, the filtrate contains impure p-toluic acid, sulfur, and acids of high molecular weight. The p-toluic acid can be recovered by distilla
tion. The filtration residue is extracted with hot dioxane, when about 20 gm of higher acids dissolve in 100 ml of the solvent. The residue consists of 4,4/-stilbenedicarboxylic acid and a small quanity of yellow-colored higher acids. Purification can be effected by the crystallization of the potassium salt from water; the ammonium and guanidine salts are equally well suited. The free acid has a m.p. of 460° and a neutraliza
tion equivalent of 134.1. The crude yield amounts to approximately 60%, calculated with respect to 51% of reacted toluic acid.
The dioxane solution contains mainly tetra(p-carboxyphenyl) thio
phene.
Example 36: Reaction between 2,4,6-trichlorophenol and sulfur (69).
2,4,6-Trichlorophenol (200 parts) is added to a cold solution of flowers
46 R. WEGLER, E. KUHLE, AND WERNER SCHAFER
of sulfur (100 parts) in oleum (30%, 100 parts); the brown solution is stirred for several hours at 10-20° and poured on to ice. The separated product is dissolved in dilute sodium carbonate solution, freed from undissolved sulfur by filtration, and reprecipitated by pouring the solu
tion into dilute hydrochloric acid. The crude product is filtered, dried, and if necessary recrystallized from glacial acetic acid or benzene.
3,3'-Dihydroxy-2,4,6,2',4',6'-hexachlorodiphenyl disulfide, m.p. 156-159°, is obtained in 93% yield as a pale yellow crystalline powder. It is readily soluble in most organic solvents as well as in dilute sodium carbonate solution.
If 2,4,6-tribromophenol is subjected to the same treatment, a good yield of 3,3'-dihydroxy-2,4,6,2',4',6'-hexabromodiphenyl disulfide is ob
tained as a yellowish crystalline powder, m.p. (after recrystallization from glacial acetic acid) 198-202°.
REFERENCES
(1) A. Plattner, "Dehydrierungen mit Schwefel, Selen und Platin-Metallen, Praparative Methoden der Organischen Chemie." Verlag Chemie, Berlin,
1943.
(2) C. Willgerodt, Ber. deut. chem. Ges. 2 0 , 2467 (1887).
(3) M . Carmack and M . A. Spielman, "Organic Reactions," Vol. 3. Wiley, New York, 1946.
(4) H. Kaltwasser, Chem. Tech. (Berlin) 9 , 392 (1957); comprehensive review of the Willgerodt reaction.
(5) C. Willgerodt, Ber. deut. chem. Ges. 2 1 , 534 (1888).
(6) L. F. Fieser and G. W . Kilmer, / . Am. Chem. Soc. 6 2 , 1354 (1940).
(7) L. Cavalieri, D. B. Pattison, and M . Carmack, / . Am. Chem. Soc. 6 7 , 1783 (1945).
(8) G. Du Pont, R. Doulou, G. Clement, and N. G. Martinez, Compt. rend, acad. sci. 2 3 9 , 178 (1954).
(9) D. F. De Tar and M . Carmack, J. Am. Chem. Soc. 6 8 , 2029 (1946).
(10) J. A. King and F. H. McMillan, J. Am. Chem. Soc. 6 8 , 525 (1946).
(11) M . Carmack and D. F. De Tar, J. Am. Chem. Soc. 6 8 , 2029 (1946).
(12) O. Wallach, Ann. Chem. Liebigs 2 5 9 , 300 (1890).
(12a) Cf. also the synthesis of auramine from 4,4'-bisdimethylaminodiphenyl-methane, sulfur and ammonia, according to the method of A. Feer, German Patent 53614 (1889); P. Friedlander, "Fortsehritte der Teerfarbenfabrikation und verwandter Industriezweige," Vol. 2, p. 60. Springer, Berlin, 1887-1890.
(13) K. Kindler, Ann. Chem. Liebigs 4 3 1 , 187 (1923).
(14) K. Kindler, Arch. Pharm. 2 6 5 , 389 (1927); German Patent 405675 (1923);
P. Friedlander, "Fortschritte der Teerfarbenfabrikation und verwandter In
dustriezweige," Vol. 14, p. 372. Springer, Berlin, 1921-1925. K . Kindler and W. Peschke, Arch. Pharm. 2 7 0 , 340, 347 (1932); 2 7 2 , 236 (1934); K. Kindler and T. Li, Ber. deut. chem. Ges. 7 4 , 321 (1941).
(14a) Y . Kawaoka, J. Soc. Chem. Ind. Japan 4 3 (Suppl. 151) (1940); R. C. Mans
field, J. Org. Chem. 2 4 , 1375 (1959).
T H E R E A C T I O N S O F S U L F U R 47
(15) E. Schwenk and L. Bloch, / . Am. Chem. Soc. 64, 3051 (1942).
(16) Morpholine is also attacked by sulfur to some extent, yielding dithiooxalyl morpholide via a partial fission (89).
(17) P. Chabrier and S. Renard, Compt. rend. acad. sci. 228, 850 (1949); Soc.
Marocaine de Procedes, Genot-Boulanger-Dausse, French Patent 1031 571 (1950).
(17a) British Hydrocarbon Chemicals Ltd., A. McLean, J. Habeshaw, and W . J.
Oldham, British Patent 797986 (1955).
(18) M . S. Newman and H. S. Lowrie, / . Am. Chem. Soc. 76, 6196 (1954).
(19) F. H. McMillan, J. Am. Chem. Soc. 70, 868 (1948).
(20) Rohm and Haas, C. L. Levesque, U. S. Patent 2560296 (1948).
(21) Farbwerke Hoechst, formerly Meister Lucius and Bruning, German Patent 99542 (1897).
(30) J. Stanek, Chem. listy 45, 224 (1951); Chem. Abstr. 46, 2528 (1952).
(31) O. Wallach, Ann. Chem. Liebigs 259, 300 (1890); Farbwerke Hoechst, Ger
man Patent 57963 (1890); P. Friedlander, "Fortsehritte der Teerfarben
fabrikation und verwandter Industriezweige," Vol. 3, p. 86. Springer, Berlin, 1890-1894.
(32) Y . Yukawa and Y. Kishi, Nippon Kagaku Zasshi 72, 371 (1951); Chem.
Abstr. 46, 7061 (1952).
(42) H. Erdmann, Ann. Chem. Liebigs 362, 133 (1908).
(43) B. Bottcher, German Patent 855865 (1942); Chem. Zentr. p. 1594 (1954);
German Patent 869799 (1940); Chem. Zentr. p. 4413 (1953).
(44) B. Bottcher and A. Luttringhaus, Ann. Chem. Liebigs 557, 89 (1947).
(45) A. Luttringhaus, H. B. Konig, and B. Bottcher, Ann. Chem. Liebigs 560, 201 (1948).
(46) B. Bottcher, Chem. Ber. 81, 376 (1948).
(47) B. Bottcher and F. Bauer, Ann. Chem. Liebigs 568, 227 (1950).
(48) Comprehensive review: F. Bauer, Chemiker-Ztg. 75, 623 (1951).
(49) N. Lozac'h and L. Legrand, Compt. rend. acad. sci. 234, 1291 (1952).
48 R. WEGLER, E. KUHLE, AND WERNER SCHAFER
(50) A. Luttringhaus, H. B. Konig, and B. Bottcher, Ann. Chem. Liebigs 5 6 0 , 201 (1948).
(51) E. Baumann and E. Fromm, Ber. deut. chem. Ges. 3 0 , 110 (1897); Farben-fabriken formerly F. Bayer and Co., German Patent 87931 (1895); P. Fried
lander, "Fortschritte der Teerfarbenfabrikation und verwandter Industrie
zweige," Vol. 4, p. 1328. Springer, Berlin, 1894-1897.
(52) Gulf Research and Development Comp., D. R. Stevens and S. C. Camp, U. S. Patent 2786829 (1952).
(52a) Y . Mollier and N. Lozac'h, Bull. soc. chim. France p. 651 (1958).
(52b) Standard Oil C o , Inventor, E. K. Fields, U. S. Patent 2857399 (1956).
(53) L. Legrand, Y . Mollier, and N. Lozac'h, Bull. soc. chim. France 2 0 , 327 (1953); Y. Mollier and N. Lozac'h, ibid. 1 9 , 1076 (1952).
(54) J. Schmitt and A. Lespagnol, Bull. soc. chim. France 1 7 , 459 (1950).
(55) Dr. A. Wander A G , German Patent 909097 (1951); Chem. Zentr. p. 10104 (1954).
(56) O. Gauding, U. S. Patent 2688620 (1951); the contents are almost identical with B. Bottcher, German Patent 869799 (1940).
(57) F. Wesseley and A. Siegel, Monatsh. Chem. 8 2 , 607 (1951).
(58) G. A. Barbaglia, Ber. deut. chem. Ges. 1 7 , 2654 (1884).
(58a) B. Tornetta, Ann. chim. (Rome) 4 8 , 577 (1958).
(59) E. K. Fields, J. Am. Chem. Soc. 7 7 , 4255 (1955); on repeating this work, R. Wegler and E. Regel found that only p-methylisopropylbenzene reacted readily, but that isopropylbenzene itself did not.
(60) N. Lozac'h and M . Denis, Bull. soc. chim. France 2 0 , 1016 (1953).
(61) B. Bottcher, German Patent 861846 (1945); Chem. Zentr. p. 7939 (1953).
(61a) F. Asinger and M . Thiel, Angew. Chem. 7 0 , 667 (1958).
(64c) F. Asinger, M . Thiel, G. Hippert, R. E. Plessmann, and J. Mennig, Angew.
Chem. 7 0 , 372 (1958).
(64d) Leuna-Werke, H. Schade and M . Thiel, German Patent 1063602 (1957).
(64e) Leuna-Werke, F. Asinger, M . Thiel, and H. Hauthal, German Patent 1068171 (1957).
(65) O. Rohm, German Patent 262707 (1912).
(66) H. Reinhardt and J. Szurrat, Gummi u. Asbest 1 0 ( 8 ) , 422-466 (1957).
(67) L. Haitinger, Monatsh. Chem. 4 , 165 (1883); S. Onufrowicz, Ber. deut. chem Ges. 2 3 , 3355 (1890); M . Lange, ibid. 2 1 , 260 (1888); Gesellschaft Chim.
Ind, Basel, German Patent 379003 (1921); Swiss priority (1920); Farben-fabriken Bayer A G , German Patent 400242 (1920); German Patent 409783
(1921); C. Ellis, U. S. Patent 1636596 (1922).
(68) K. A. Hofmann, Ber. deut. chem. Ges. 3 8 , 1432 (1905); G. Schultz and H. Beyschlag, ibid. 4 2 , 743 (1909).
(69) Farbenfabriken Bayer A G , W . Retter and W . Miiller, German Patent 1024089 (1955).
(70) R. Geigy, German Patent 86874 (1895); P. Friedlander, "Fortschritte der Teerfarbenfabrikation und verwandter Industriezweige," Vol. 4, p. 136.
Springer, Berlin, 1894-1897.
T H E R E A C T I O N S O F S U L F U R 49
(71) Farbwerke Hoechst formerly Meister Lucius and Briining, German Patent 106509 (1898).
(72) M . J. J. Blanksma, Rec. trav. chim. 2 8 , 109 (1909); J. van der Lee, ibid. 4 5 , 678 (1926).
(73) Fiat Final Report No. 1313, London; "German Dyestuffs and Dyestuffs Intermediates," Vol. 1, p. 20.
(74) Monsanto Chemical C o , O. De Garmo and E. J. McMullen, U. S. Patent 2795614 (1953).
(75) M . M . L. Aronstein and A. S. van Nierop, Rec. trav. chim. 2 1 , 448 (1902).
(76) B. Emmert and M . Groll, Chem. Ber. 8 6 , 205 (1953); 8 6 , 208 (1953).
( 7 7 ) B. Emmert and A. Holz, Chem. Ber. 8 7 , 676 (1954).
(77a) For further work on the reaction between a- or y-methylated pyridine and amines, see B. Emmert, Chem. Ber. 9 1 , 1388 (1958).
(82) Dahl and C o , German Patent 47102 (1888); German Patent 35790 (1885).
(83) L. Gattermann, Ber. deut. chem. Ges. 2 2 , 422 (1889); Fiat Final Report No.
1313, London; "German Dyestuffs and Dyestuff Intermediates," Vol. I, p.
126.
(84) A. Green, Ber. deut. chem. Ges. 2 2 , 968 (1889); Kalle and C o , German Patent 61204 (1891).
(85) W . Zerweck, H. Ritter, and M . Schubert, Angew Chem. 6 0 , 141 (1948).
(86) Farbenfabriken Bayer A G , W . Schafer and R. Wegler, German Patent 964142 (1953).
(87) Farbenfabriken Bayer A G , W . Schafer and R. Wegler, German Patent, Specification F.17140 (1955).
(88) H. D. Porter, J. Am. Chem. Soc. 76, 127 (1954).
(89) R. L. Malan and P. M . Dean, / . Am. Chem. Soc. 6 9 , 1797 (1947).
(90) Farbenfabriken Bayer A G , German Patent 51172 (1889); P. Friedlander,
"Fortschritte der Teerfarbenfabrikation und verwandter Industriezweige,"
Vol. 2, p. 301. Springer, Berlin, 1887-1890.
(91) H. Najer, P. Chabrier, R. Giudicelli, and E. Joannic-Voisinet, Compt. rend, acad. sci. 2 4 4 , 2935 (1957).
(92) J. Schmitt and M . Suquet, Bull. soc. chim. France 2 3 , 755 (1956).
(93) B. Holmberg, Arkiv Kemi Mineral. Geol. 17A(23), 1-10 (1944).
(94) R. C. Moreau, Bull. soc. chim. France 2 2 , 918 (1955).
(95) Farbenfabriken Bayer A G , W . Schafer, G. Domagk, and R. Wegler, German Patent, Specification F.12625 (1953); Farbenfabriken Bayer A G , see also Austrian Patent 191426 (1954).
(96) H. Schmidt, R. Behnisch, F. Mietzsch, and G. Domagk, Naturwissenschaften 3 3 , 314 (1946) (14 patent specifications); Hoffman La Roche and C o , Swiss Patent 288024 (1950).
(97) Farbenfabriken Bayer A G , E. Kuhle, W . Schafer, and R. Wegler, German Patent—Specification F.14355 (1954); see also Farbenfabriken Bayer A G , Austrian Patent 191426 (1954).
50 R. WEGLER, E. KUHLE, AND WERNER SCHAFER
(98) Farbenfabriken Bayer A G , E. Kuhle and R. Wegler, U. S. Patent 2774757 (1955).
(99) This product is identical with a comparison sample prepared from thioiso-nicotinic acid hydrazide (prepared by Dr. Konig, Wuppertal-Elberfeld) and y-pyridinealdehyde.
(100) M . A. Naylor and A. W . Anderson, / . Am. Chem. Soc. 75, 5395 (1953).
(101) DuPont, M . A. Naylor, Jr., U. S. Patent 2610980 (1949); see also U. S.
Patent 2695312 (1953).
(102) DuPont, M . A. Naylor, Jr., U. S. Patent 2744134 (1950).
(103) California Research Corp, W . G. Toland, U. S. Patent 2587666 (1950); simi
lar to German Patent 1003712 of the same firm (1954).
(104) N. V. De Bataafsche Petroleum Maatschappij, German Patent 1004603 (1954); German Patent 1007761 (1955); German Patent 1008279 (1955).
(105) California Research Corp, W . G. Toland, Jr., U. S. Patent 2722547 (1951).
(106) California Research Corp, British Patent 719695 (1951); U. S. Priority (1950).
(107) California Research Corp, W . G. Toland, Jr., U. S. Patent 2783266 (1953).
(107a) California Research Corp, W . G. Toland, Jr., U. S. Patent 2845449 (1956).
(108) California Research Corp, W . G. Toland, Jr., German Patent—Specification C 9390 (1954).
(110) Winthrop Stearn, J. A. King, U. S. Patent 2459706 (1945).
(110a) R. Lantz, G. Mingarson, and H. Delarne, Bull. soc. chim. France p. 1201 (1957).
(111) Rohm and Haas, C. L. Levesque, U. S. Patent 2489094 (1948).
(111a) Ruhrchemie A G , H. Feichtinger, German Patent 1003212 (1955).
(111b) BASF, A. Hrubesch, and H. Friederich, German Patent 1042574 (1956).
(112) J. Schmitt and M . Suquet, Bull. soc. chim. France 23, 755 (1956).
(113) Rohm and Haas, C. L. Levesque, U. S. Patent 2525075 (1948).
(114) DuPont, M . J. P. Hartig, U. S. Patent 2631166 (1952) (special working-up process).
(115) M . A. Naylor and A. W . Anderson, / . Am. Chem. Soc. 75, 5392 (1953).
(116) DuPont, M . A. Naylor, Jr, and H. A. Straw, U S. Patent 2640077 (1951);
U. S. Patent 2640078 (1951).
(116a) Ruhrchemie A G , H. Feichtinger and H. Tummes, German Patent 929192 (1952).
(116b) Ruhrchemie A G , H. Feichtinger, H. Kolling, and S. Puschhof, German Patent 899799 (1951).
(116c) Ruhrchemie A G , H. Feichtinger and H. Tummes, German Patent 929191 (1952).
(116d) Ruhrchemie A G , H. Feichtinger and S. Puschhof, German Patent 873840 (1951).
(116e) Ruhrchemie A G , K. W . Schneider and H. Feichtinger, German Patent 871755 (1950).
(116f) Ruhrchemie A G , H. Feichtinger, German Patent 877605 (1950).
T H E R E A C T I O N S O F S U L F U R 51
(117) Ruhrchemie AG., H. Feichtinger, German Patent—Specification R.4614 (1950).
(117a) Goodyear Tire and Rubber Comp, J. Kamlet, U. S. Patent 2826609 (1954).
(118) Survey of the literature: J. van Alphen, Angew. Chem. 66, 193 (1954).
(119) E. H. Farmer, Trans. Faraday Soc. 38, 340 (1942).
(120) E. H. Farmer and F. W . Shipley, J. Chem. Soc. p. 1519 (1947).
(120a) L. Batemann, R. W . Glazebrook, C. G. Moore, M . Porter, G. W . Ross, and R. W . Saville, Rubber Chem. and Technol. 31, 1055 (1958).
(121) G. F. Bloomfield, India Rubber / . 1 1 1 , 277, 313 (1945).
(122) W . Scheele and M . Cherubim, Kautschuk u. Gummi 10(8), W T 185 (1957).
(123) H. Krebs, Angew. Chem. 64, 360 (1952).
(124) S. Kambata and K. Ohkita, Rubber Chem. and Technol. 25, 209 (1952).
(125) W . Scheele, 0 . Lorentz, and W . Dummer, Kautschuk u. Gummi 8(1), W T 2 (1955); W . Scheele, O. Lorentz, and W . Dummer, 8(2), WT27 (1955);
W. Scheele and G. Beilstein, 8(10), WT251 (1955).
(126) J. R. Geigy, French Patent 1134253 (1955); Swiss priority (1954).
(127) Ann. Chem. Liebigs 494, 57 (1932).
(128) R. Wegler, Experimental directions by the Wiss. Hauptlaboratorium der Farbenfabriken Bayer A G , Leverkusen.
(129) W . Schafer, Experimental directions by the Wiss. Hauptlaboratorium der Farbenfabriken Bayer A G , Leverkusen.
(130) California Research Corp, H. J. Aroyan and J. B. Wilkes, German Patent 1014096 (1955).