Chloroazobenzenes: Studies on Syntheses

1 downloads 0 Views 3MB Size Report
Nov 24, 2015 - Reduction by LiAlH4 was the method of choice, but it proved inadequate for the syn theses of chloroazobenzenes from o-chloronitrobenzenes.
994

H. A. B. LINKE. R. BARTHA. AND D. PRAMER

Chloroazobenzenes: Studies on Syntheses H. A. B. L in k e , R. B a r t h a , and D. P r a m e r * Department of Biochemistry and Microbiology. Rutgers University, New Brunswick, New Jersey 08903, USA Dedicated to Prof. Dr.

Otto N eunh o effer

on his 65-th birthday

(Z. Naturforschg. 24 b, 994—996 [1969] ; eingegangen am 19. Februar 1969)

Thirteen chloroazobenzenes were synthesized by reduction of chloronitrobenzenes or by oxidation of their corresponding chloroanilines. Five of the compounds have not been previously prepared or described. Reduction by LiAlH4 was the method of choice, but it proved inadequate for the syn­ theses of chloroazobenzenes from o-chloronitrobenzenes. This reaction eliminated chlorine if ortho to the aniline nitrogen and an additional chlorine atom ; in the other cases steric hindrance of azo bond formation resulted in low yields. Chromatographic systems for the separation of pure chloro­ azobenzenes from the crude reaction mixtures were developed and are described.

R esults and D iscussion The synthesis of chloroazobenzenes depends in part on the starting m aterial. Som e m ethods are based on o x id a tio n o f the am ino group o f chloro­ an ilin es and others require the reduction o f the nitro group of chloronitrobenzenes. E d w a r d 1 oxid ized prim ary arom atic am ines to azobenzenes u sin g benzoylp eroxid e (y ield 5 — 2 0 % ). T he oxid an t used by W h e e le r and G o n z a l e s 2 w as M n 0 2 (y ield 5 to 9 0 % ); and they observed that h alo g en o a n ilin es su b ­ stituted in the p -p osition w ere esp ecially reactive in the order F > C l > B r > I . D a n i e l s and S a u n d e r s 3 produced 4 ,4 /-dichloroazobenzene (y ield 20% ) en zy­ m atically in a system that con tain ed p-chloroaniline, H 20 2 and horserad ish p eroxid ase in acetate buffer at pH 4 .6 . K r e m e r and B e n d ic h 4 reduced chloro­ nitrobenzenes to chloroazobenzenes (yield 4 0 — 80%) and other products w ith m on oeth an olam in e in the presence of anh yd rou s Na 2C 0 3 , but reduction with L iA lH 4 in ether so lu tio n as described by C o r b e t t and H o l t 5 proved to be a sup erior m ethod for the synthesis of chloroazobenzenes (y ield up to 9 5% ). H ow ever, present results in d icate that this m ethod is not suitable for p roduction o f chloroazobenzenes from o-chloronitrobenzenes. C hlorine that w as ortho to the nitro group and an ad d ition al chlorine atom , w as elim inated in the course o f the reaction. C hlorine ortho to the nitro group and w ithout an adjacent * Dept, of Biochem. and Microbiol, and the Bur. of Conser­ vation and Environmental Sei., Rutgers-The State Univer­ sity, New Brunswick, New Jersey 08903, USA. 1 J. T. E d w a r d . J. chem. Soc. [London] 1956. 2 2 2 . 2 O. H. W h e e l e r and D. G o n z a l e z , Tetrahedron [London] 20. 189 [1964],

chlorine atom was n ot elim inated, b ut the yield of dichloroazobenzene was low ( < 5 % ) . N itrobenzenes w ith chlorine substitutents in m eta an d /o r para p o si­ tion produced azo com pounds in yields as g reat as 95 per cent. These differences can be explained only by steric hindrance. A pparently, a halogen atom ortho to an am ino or nitro gro u p interferes sterically w ith the form ation of an azo bond. D a i n s and K e n y o n 7 also noted halogen losses when su b ­ stituted arom atic n itro and n itro so com pounds were reduced to azoxybenzenes w ith sodium alcoholates. Losses am ounted to as much as 62 per cent. They were not a function of location of the halogen but depended on the n atu re of the alcohol used. Some of the reactions yielded quantities of tar, so th at purification of chloroazobenzenes p resented d if­ ficulties. The physical p ro p erties of chloroazoben­ zenes, chlorohydrazobenzenes and chloroazoxybenzenes are very sim ilar, b u t they were sep arated by chrom atography on n eu tral alum inum oxide (W oelm, Act. I) colum ns that were developed by n onpolar solvents (ligroine, benzene, to lu en e). E f­ fluents were fractionated and exam ined by gas chro­ m atography for di-, tetra- and hexachloroazobenzenes (DCAB, TCAB. H C A B ). As a final step in the purification of all azob en zen es* * , the com pounds were recrystallized from acetone and th eir homogenity was established by thin layer and gas chro­ m atography. 3

4

D . G. H. D a n i e l s a n d B. C. S a u n d e r s , J. diem. S o c . [L o n ­ d o n ] 1953,822. C h . B. K r e m e r a n d A. B e n d i c h , J. Amer. chem. Soc. 62,

1279 [1940], 5 J. F. C o r b e t t a n d P. F. H o l t , J. diem. S oc. [L o n d o n ] 1963, 2385.

Unauthenticated Download Date | 11/24/15 4:07 AM

CHLOROAZOBENZENES: STUDIES ON SYNTHESES

T he azobenzenes synthesized are listed in Table I. Com pounds 2, 3, 4, 6, 7, 9, 10, and 12 were p ro ­ duced from th eir corresp o n d in g chloronitrobenzenes

mp [°C]

Azobenzene 2,2'-DichloroS.S'-Dichloro4,4'-Diehloro2,2',3,3'-Tetrachloro2,2/,4,4/-Tetrachloro2,2',5,5'-Tetrachloro2,2',6,6'-Tetrachloro3,3',4,4'-Tetrachloro3,3',5,5'-TetrachloroS ^'-D ich lo ro ^ ^ '-d im eth y l2,2',4,4',5,5/-Hexachloro2,2/,4,4',6,6'-Hexachloro-

( 1) (2) (3) (4) (5) (6) (7) (8)

(9) ( 10) ( 11) ( 12) (13)

68 1 3 3 -1 3 4 1 0 1 -1 0 2 1 8 4 -1 8 5 2 0 4 -2 0 5 1 6 7 -1 6 8 1 9 0 -1 9 1 128 158 1 9 3 -1 9 4 1 3 2 -1 3 3 2 1 6 -2 1 7 193

Refer.

1. 2, 9 5 5 1, 2, 3, 5 to, e,

1 5

b 4, 5, 8 4, 5

b b b

Table I. Some azobenzenesa and their melting pointsd. a The UV- and IR-spectra indicated that all compounds were ?rarcs-isomers. New compounds. c See reference 6. d For UV and IR characterization see reference 11.

by red u ction w ith excess LiA lH 4 in ether. Since it was not possible the obtain com pound 5 by this p ro ­ cedure, it was synthesized by m ild reduction of 2,3Yields obtained Azo­ R educt, of Synthesis ben­ chloronitro­ by other benzenes m ethods zene w ith LiA lH 4 1

2

3 4 5

6 7

8

9

10 11 12 13

_ 40 80 80 dehalog. 20 20 < 0 .1 80 80 —

5



>

9 L. G a t t e r m a n n and H. W i e l a n d , „Die Praxis des organi­ schen Chemikers“, p. 163, Walther de Gruyter & Co., Ber­ lin 1956. 10 A. I. V o g e l , Textbook of Practical Organic Chemistry, p. 199. Longmans Green, London 1948. 11 H. A. B. L in k e and D. P r a m e r , Submitted for publication in Z. Naturforschg., Teil b.

Unauthenticated Download Date | 11/24/15 4:07 AM

996

CHLOROAZOBENZENES: STUDIES ON SYNTHESES

lized from acetone. Red needles, m p: 204 —205 °C. Yield: 5 per cent. Anal. Calcd for C 12H 6N 9C14: C 45.02; H 1.89; N 8,76; Cl 44.33. Found: C 45.09; H 1.85; N 8.91; Cl 44.23. 2,2',6,6'-Tetrachloroazobenzene ( 8) : 5 g 2,6-dichloroaniline and 15 g freshly prepared lead tetraacetate 10 were reacted in the cold (ice bath) with stirring for 1 hour. The precipitate was collected by filtration and washed with benzene. The benzene washes were com­ bined with the filtrate, the solution was treated with Na 2C 0 3 and anhydrous N a 2S 0 4 and refiltered. The benzene filtrate was evaporated to dryness, and the residue was dissolved in ligroin (60 —70 °C) and p u ri­ fied by column chromatography as described for com­ pound 5, with the addition of elution with benzene; the bulk of 8 was eluted by the benzene. The eluate was dried by evaporation, the residue was dissolved in toluol and rechromatographed on neutral aluminium oxide (Woelm, Act. I) column that was developed with toluol. Fractions of the eluate containing 8 were com­ bined, evaporated to dryness and the compound was recrystallized from methanol and acetone. Green plates, mp: 128 °C. Yield: 5 per cent. Anal. Calcd for C 12H 6N 2C14: C 45.02; H 1.89; N 8.76; Cl 44.33. Found: C 45.09; H 1.84; N 8.84; Cl 44.48. 3,3-Dichloro-4,4-dimethylazobenzene (11) : To 3.5 g 3-chloro-4-methylaniline dissolved in 150 ml benzene, 10.8 g activated M n 0 2 were added. The reaction mix­ ture was refluxed for 10 hours. The insoluble residue was collected by filtration, extracted with hot benzene, and the filtrate and washes were combined, concen­ trated by evaporation and compound 11 crystallized when cold acetone was added. Recrystallized from ace­ tone. Orange needles, m p: 132 —133 °C. Yield: 75 per cent.

Anal. Calcd for C 14H 12C12N 2: C 60.23; H 4.33; N 10.03; Cl 25.41. Found: C 60.53; H 4.54; N 9.27; Cl 25.38. 2.2 ',4,4',5,5-Hexachloroazobenzene (12) : To an icecooled solution of 12 g 2,4,5-trichloronitrobenzene in 150 ml anhydrous ether, 6 g LiAlH 4 suspended in 150 ml of cold anhydrous ether were added dropwise with constant stirring. After 2 hours at room tem pera­ ture, the reaction mixture was refluxed for 15 minutes and cooled. Excess LiAlH 4 was destroyed by the dropwise addition of H 20 , and the ether phase was se­ parated and evaporated to dryness. The residue was dissolved in ligroin (60 —70 °C) and transferred to a 30 cm neutral aluminium oxide column (Woelm, Act. I ) . The column was developed first with ligroin and then with benzene. Gas chromatographic analysis de­ monstrated that the benzene eluate contained the bulk of 12. This material was evaporated to dryness and the product was recrystallized from acetone. Orange need­ les. mp: 216 —217 cC. Yield: 5 per cent. Anal. Calcd for C 12H 4N 2C16: C 37.04; H 1.04; N 7.21; Cl 54.71. Found: C 37.13; H 1.27; N 7.61; Cl 53.41. ^ 2.2 ,4,4,,6,6'-Hexachloroazobenzene (13) : 4.9 g 2,4,6-trichloroaniline in 150 ml benzene were refluxed for 10 hours with 10.8 g activated M n 0 2 . The reaction product was purified by the procedures described for compound 11 and recrystallized from an ether-acetone mixture. Red-brown needles, mp: 193 °C. Yield: 20 per cent. Anal. Calcd for C12H 4N,C16: C 37.04; H 1.04; N 7.20; Cl 54.72. Found: C 37.04; H 1.04; N 7.20; Cl 54.38. We thank the Upjohn Company for the gift of 2,4,5-trichloroaniline. The work described in this paper of the Journal Series, New Jersey A gricultural Experi­ ment Station, was supported in part by USPHS Re­ search Grant ES-16.

Unauthenticated Download Date | 11/24/15 4:07 AM