摘要:
2674 J. Chem. SOC. (C), 1970 Synthesis of Azine Perhalide Adducts By F. L. Scott* and P. A. Cashell, Chemistry Department, University College, Cork, Ireland Bromine reacts with para-substituted benzaldehyde azines in anhydrous acetic acid, to form substituted azinium perbromides (AzineHf Br3--) in good yields. Chemical (positive bromine analysis, as well as the ability of the azinium perbromide t o brominate aromatic nuclei), and physical (Lr. and n.m.r.). data support t h e structure we pro- pose for these compounds. Tri-iodide ion also forms a similar compound with benzaldehyde azine in glacial acetic acid, whereas chlorine reacts with the azine to form a dichloromethine-substituted product. BROMINE forms two types of complexes with molecules structure has been formulated both as AmBr, and which contain donor nitrogen atoms, such as pyridine 2, AmBr+ Br-, though recently the former covalent fomu- quinoline 3, oxazolines *, etc.The first of these has the lation has been l refer red.^ The second type of complex stoicheiometry AmBr, (Am = donor amine) and its has the stoicheiometry and structure of AmH+ Br3-. In the case of the best studied examples of both types, i.e. K. W. Rosenmund and W. Kuhnhenn, Clzem. Ber., 1923, 56, 1262. Preliminary communication, F. L. Scott and P. A. Cashell, (a) R. Lombard and G. H:ywang, Bull. Sac. d i m . France: Chem. and Ind., 1969, 1343. 1952, 331; (b) 2. E. Jolles, Bromine and its Compounds, K.-D. Hesse and W. Seeliger, Annalen, 1969, 724, 166. London, Benn, 1966, pp. 73, 345, 368-389. 0. Hassel and C.Rermming, Qwart. Rev., 1962, 16, 1.Org. 2675 those of pyridine, the latter type of complex, i.e., pyridinium perbromide is much more stable than the pyridine bromine adduct. The bromine adducts of open-chain imino-compounds reported to date have all been of the first type. Thus, Gibson has found that arylidene-2-pyridylhydrazones (Hy) form complexes with bromine of type HyBr+ Br-, and more recently, Walia has established that the bromine adducts of Schiff bases-originally formulated * as the covalent adducts ArCHBr,NBrAr'-are N- bromoimmonium bromides [ArCH=NBrAr'] +Br-. We now report the first open-chain complexes of the per- bromide type, namely azinium perbromides (I). These were obtained as pure crystalline products in good yield upon the addition of two molecular equivalents of bro- mine to one of azine in anhydrous acetic acid at ambient temperature.rArCH=&-N=CHArI Br,- PhC=N-N=CPh 1 c1 I c1 The structures of these materials were established Br,- both by chemical and physical means. The chemical tech- niques involved first a quantitative evaluation of the oxidising bromine content the perbromides possessed. (This quality incidentally was elusive, the azine per- bromides losing bromine gradually with time and show- ing significant deterioration in 1-2 months even when kept in vacuo in the presence of a drying agent). To estimate the active bromine content of these materials, they were treated with an excess of iodide ion in meth- anol, to give two equivalents of i ~ d i n e . ~ This was titrat ed amperometrically with aqueous thiosulphat e, using a diffusion current between two platinum electrodes to determine the iodine present.All six azinium per- bromides gave results consistent with the proposed struc- ture. Of critical importance to this structural assign- ment is the fact that when the azinium perbromides were partitioned between ether and water, the azines were re- covered generally in excellent (290%) yields from the ethereal layer, thus establishing that the bromine addi- tion to form compounds (I) is easily reversible. M. S. Gibson, Tetrahedron, 1963, 19, 1587. J. S. Walia and P. S. Walia, Chew and Ind., 1969, 135. 8 Nasir-ud-Din, Hasibullah, M. Latif, and A. Saeed, Chewz. and Ind., 1967, 1875. R. E. Buckles, B. T. Simpson, and W. F. Edgell, J .Org. Chem., 1958, 23, 483. J. Elguero, R. Gil, and R. Jacquier, Sfiectrochiluz. Acta, 1967, 2314, 383. 11 The azomethinyl hydrogen of benzaldehyde azine appears a t T 1.45 (in carbon tetrachloride); see J. W. Emsley, J. Feeney, and L. H. Sutcliffe, ' High Resolution Nuclear Magnetic Reson- ance Spectroscopy,' Pergamon, Oxford, 1966, vol. 2, p. 1115. The physical confirmation of structure involved both i.r. and n.m.r. spectroscopy. The i.r. spectra of all six parent aldazines showed strong absorption at 1620- 1630 cm-l due to C=N stretching, as expected.l* This absorption shifted when the azine hydrobromides were used as substrates to 1660-1665, due to C=NHf stretch- ing. Interestingly, this occurred even though only one of the azine nitrogens was protonated; it is also of interest that the shift appears the same whether H+ or Br+ is added to nitrogen, C=NBr+ stretching being re- corded a t ca.1650 cm-l.7 Finally, all six azinium per- bromides showed absorption at 1655 cm-l although as has just been mentioned, this in itself does not distinguish between C=NH+ and C=NBr+ stretchings. The lH n.m.r. spectrum in perdeuterioacetic acid of benzalde- hyde azine shows a singlet at T 1.33 ( c j . ref. 11) due to a methine proton signal, CH=N. In benzaldehyde azin- ium perbromide, this proton signal is a t T 0.59, corre- sponding to the proton signal in CH=NH+. This kind of shift was also shown by Walia's compounds (T for CH=NBr+ was 0.55) and by Olah l2 for imine protonation. Our structural picture of the bonding in compounds (I) is further supported by the fact that benzaldehyde azine hydrobromide was isolated as an intermediate when bromine was added to benzaldehyde azine in acetic acid in insufficient quantity for complete reaction to form the perbromide.Furthermore, when benzaldehyde azine hydrobromide was treated with bromine in acetic acid, the azinium perbromide was formed. This reaction is analogous to that of Djerassi l3 for the preparation of pyridinium perbromide. Two interesting aspects of the chemistry of benzalde- hyde azinium perbromide, and by analogy of the other azinium perbromides, were briefly explored. The first involved hydrolysis of the parent perbromide in 70% acetic acid to give benzaldehyde and benzaldehyde azine in a ca. 1 : 1 ratio; the kinetics and mechanism of this oxidative cleavage will be described e1~ewhere.l~ The second was the behaviour of the parent perbromide as a brominating agent.Thus, in warm acetic acid it brominated acetanilide and aniline to give high yields of the 4-bromo- and 2,4,6-tribromo-compounds respec- tively, benzaldehyde azine being recovered in good yield. Reaction of the parent perbromide with an excess of iodide ion in anhydrous acetic acid gives the correspond- ing azinium periodide (11), a compound also prepared by treating benzaldehyde azine with iodine in the presence of iodide ion in acetic acid. Chlorination of benzalde- hyde azine in acetic acid gave the substitution product, the dichlorinated azine (111). This procedure is far more convenient for the preparation of (111) than those previously emp10yed.l~ One anomaly remains in the reactions of aldazines 12 G.A. Olah and P. Kreienbuhl, J . Amer. Chem. SOC., 1967, l3 C. Djerassi and C. Scholz, J . Amer. Chem. SOL, 1948, 70, 14 F. L. Scott and P. A. Cashell, unpublished results. 15 K. Issleib and A. Balszweit, Chem. Ber., 1966, 99, 1316. 89, 4756. 417,2676 J. Chem. SOC. (C), 1970 with bromine. Thus, both CurtiusI6 and Stollel' re- ported the formation of a tetrabromide when aromatic aldazines were brominated in carbon tetrachloride or chloroform. These they formulated as purely covalent adducts. The parent compound which was difficult to obtain pure (from benzaldehyde azine) regenerated the azine quantitatively when portioned between ether and water ; thus, the previous formulations implying irre- versible bromine addition were incorrect.The i.r. spectrum of the tetrabromide was essentially that of the corresponding azinium perbromide, and its IH n.m.r. again showed a proton signal a t z 0-59. Its active bromine analyses were anomalous and gave values close to 1.5 equivalents of active bromine per mole of azine. If the compound had the structure we anticipated, namely (IV), then an oxidising equivalent of 2 would be expected. We cannot, as yet, offer a complete struc- tural picture for these rather unstable tetrahalogen compounds. EXPERIMENTAL M.p. s were determincd on an Electrothermal melting point apparatus. 1.r. spectra were recorded on a Perkin- Elmer Infracord model 137, and a Perkin-Elmer Spectro- photometer model 457, as KBr and CsI discs.U.V. spectra Yield Ar M.p. (%I Ph 137' 67 p-Pr'C,H, 110 58 p-MeOC,H, 164-165 66 P-h!kC& 180-181 68 p-C1C,H4 212-214 68 $-BrC,H, 216-217 69 difference of ca. 102 mV) . N-Bromoacetamide, N-bromo- succinimide, and pyridinium perbromide, were first titrated as standards, each one of them possessing one active bromine atom per molecule. These standards and the six azinium perbromides yielded results indicative of the presence of one active bromine atom per molecule. These results were as follows : N-bromoacetamide, 0.994 ; N-bromosuccinimide, 1.00; pyridinium perbromide, 0-985; and for the azinium perbromides-[the substituent refers to the benzylidene rings, Ar, in(I)] : hydrogen, 0.989; ?-Me, 0.995; p-Pri, 0.985; p-MeO, 1-03; p-Cl, 0.972; p-Br, 0.978. Azine Regeneration from Perbromides.-For each of the six perbromides, a pre-weighed sample, (ca.200 mg), was shaken with ether-water ; the liberated azine went into the ethereal layer. The ethereal layer was separated, dried (MgSO,) , and evaporated, and the residue was dried. M.p. and mixed m.p. established that the residue was the appro- priate azine, in each case. The azine recovery yields (%) were: hydrogen, 97; p-Me, 87; p-Pri, 95; p-MeO, 92; p-Cl, 80; p-Br, 97. A similar procedure with the benzaldehyde azine tetra- bromide gave a 93% azine recovery. I.Y. data.-Some of the i.r. data which have been discussed above are summarised in Table 2. Benzaldehyde Azine Hydrobromide as Intermediate in the FormatioN of the Perbromide.-Benzaldehyde azine hydro- bromide was made by treating the azine (2.40 g, 11.5 mmol) TABLE 1 Substituted benzaldehyde azinium perbromides (I) Found (yo) I L -l 7 Formula C H N Br C C,,H,,N,,HBr, 3 7 4 3.0 6.45 53.2 37.4 C,,H,,N,,HBr, 40.3 3.8 5.8 50.8 40.2 C2,H,,N2,HBr, 45.05 4.7 5.3 45.0 45.05 C16Hl,N202,HBr3 38.0 3.4 5.6 46.75 37.8 C,,H1,M,C1,,HBr3 32-7 2.2 5.35 46.0 32.4 C,,Hl,N,Br,,HBr, 27.95 1.75 4.9 65.4 27.7 Required (%) H N Br 2.9 6.25 53.4 3.55 5.86 50.3 4.7 5.25 45.05 3.35 5.5 47.1 2-1 5.4 46.3 1.8 4.6 65.8 were recorded on a Unicam SP 800 instrument; 1H n.m.r.in ether with hydrogen bromide; it was precipitated as a spectra were recorded on a Varian HA-100, 100 MHz instru- pale yellow mass which was recrystallised from 95% ment, with CD,CO,D as solvent for benzaldehyde azine and ethanol (2.91 g, 10.1 mmol, 87%), m.p.164-165" (lit.,17 its perbromide, and in CC1, for the azine tetrabromide, using saturated solutions. Microanalytical determinations were TABLE 2 carried out by Dr. Strauss, Oxford, and Mrs. K. M. Duggan of this Department. Preparation of Azinium Perbromide.-For each preparation ca. 10 mmol of the appropriate para-substituted benzalde- hyde azine was dissolved in anhydrous Pronalys grade acetic acid, at room temperature, and slightly more than 2 molar equivalents of bromine (10% solution in acetic acid), were added dropwise, with stirring, to the azine. Almost immediately, the perbromide began to appear, as an orange crystalline precipitate. Most of the perbromides needed no further purification, and the others, (the 9-meth- oxy- and p-chloro-compounds) , were crystallised from acetic acid in the presence of excess of bromine. The yields, m.p.s and microanalytical data are given in Table 1.Iodovlzetvic Tityation.-In a typical titration, 50-100 mg of azinium perbromide was added to 0.lN-methanolic potas- sium iodide ( 1 ~ in acetic acid). The liberated iodine was titrated against aqueous thiosulphate with a simple electro- metric apparatus. The end-point was detected as zero diffusion current between two Pt electrodes, (with a potential -C=N- (stretching) frequencies for azines, azine hydro- bromides, and azinium perbromides (cm-l) Ar Azine Hydrobromide Perbromide Ph 1620 1660 1656 p-MeC,H4 1626 1661 1658 p-Pr{C,H, 1630 1664 1661 p-MeO*C,H, 1623 1667 1653 9-C1C6H, 1626 1661 1658 $-BrC,H4 1634 1661 1653 165").It was suspended in acetic acid, and slightly more than one equivalent of bromine was added dropwise during 30 min, with stirring; an orange crystalline material separ- ated (m.p. 135", mixed map. 136-137", pertinent physical data in Table 1). In the bromination of benzaldehyde azine to give the perbromide, the azine hydrobromide was isolated (70%) 16 T. Curtius and E. Quedenfeldt, J . prakt. Chem., 1898, 58, l7 R. Stolle, J . prakt. Chem., 1912, 85, 386. 372.Org. 2677 when ca. half of the stoicheiometric quantity of bromine had been added. It was characterised by its m.p. and mixed m.p. 164-165" and i.r. spectrum. Benzaldehyde Aziniunz Perbromide in 70% Acetic Acid.- Benzaldehyde azinium perbromide (471 mg, 1.05 mmol) in 70% acetic acid (50 ml, to give a 2.1 x 1 0 - 2 ~ solution, with respect to the perbromide) was stirred for 15 min, 0.125 rnl was removed with a syringe, and made up to 50 ml in n- hexane, giving a 0.525 x 1 0 - 4 ~ solution (based on the perbromide).A U.V. spectrum of the solution was run (with n-hexane containing 0.125 ml of 70% acetic acid in 50 ml as blank), and the following main absorption maxima were obtained: Am= 242 nm (A = 0-89) and A,, 299 nm (A = 0.91), which were due to benzaldehyde and benzaldehyde azine, respectively. Benzaldehyde has (n-hexane) = 1.5 X lo4, hence the concentration of benzaldehyde pro- duced was 0.585 x 1 0 - 4 ~ . Benzaldehyde azine has E,, (n-hexane) =r 3.8 x 104, hence the concentration of azine produced was 0.24 x 1 0 - 4 ~ . These represent yields of zldehyde, 56%, and azine, 45.5%. An analogous experiment was run for $-chlorobenzalde- hyde azinium perbromide, and the yields of the appropriate aldehyde and azine were 53% and 48% respectively. Brominations with Benzaldehyde A x i n i u m Peybromide.- Acetanilide: Acetanilide (214 mg, 1.58 mmol), the per- bromide (691 mg, 1.54 mmol), and acetic acid (5 ml) were heated to 50".After 10 min the mixture was allowed to cool; it was added to an excess of water (40 ml), to give a pale yellow mass. This was freed of unchanged acetanilide with warm water (50 ml, 70') and fractionally crystallised from methanol to give benzaldehyde azine (m.p., crude, 87"; mixed m.p., 89-92'; 259 mg, 81%); and $-bromoacet- anilide (m.p. 164-165'; mixed m.p. 165-168"; 284 mg, 847;).Aniline: To a stirred solution of the perbromide (1.41 g, 3-14 mmol) suspended in acetic acid (25 ml) was slowly added AnalaR aniline (0.2 ml, 204 mg, 2.2 mmol) in acetic acid (5 ml). The mixture was heated to 50" for 30 min after which it was diluted with ether (200 ml) ; 2,4,6-tribromo- aniline hydrobromide was precipitated ; m.p. and mixed m.p. 195-196" (from ethanol) (382 mg, 89%). Evapora- tion of the ethereal filtrate and addition of water gave the azine (550 mg, 84%). Formation of Aziniunz Periodide, (11) .-Benzaldehyde azinium perbromide (500 mg, 1-1 mmol) and a 0 . 1 ~ solution of potassium iodide in glacial acetic acid was stirred for 3 h at room temperature. The colour of the solution darkened, and eventually a brown precipitate was deposited. It was filtered off, recrystallised twice from acetic acid, and dried.The material had m.p. 151-153", and its analysis indicated that it was an azine tri-iodide (427 mg, 0.72 mmol, 66%) (Found: C, 28.2; H, 2.5; I, 64.25; N, 5.15. Cl,Hl,I,N2 re- quires C, 28.5; H, 2-2; I, 64.5; N, 4.75%). Its i.r. spectrum shows a shift in the C=N (stretching) absorption from 1620 cm-l in the free azine to 1640 cm-l, a feature consistent with protonation on the azine nitrogen. Benzaldehyde azinium periodide could also be made by treating benzaldehyde azine (200 mg, 0.96 mmol), with an excess of iodine in 0 - 1 ~ - potassium iodide in acetic acid, and stirring the solution for 4 h, to yield a brown precipitate, which, when recrystallised from acetic acid, gave benzaldehyde azinium periodide, as before, (m.p.151-153"; 392 mg, 69%). Its i.r. spectrum was identical to that for the periodide obtained from the reaction described above, and a mixed m.p. of the two was not depressed. Pveparation of aa'-Dichlorobenzaldelzyde A z i n e (111) .- Benzaldehyde azine, (10.4 g, 50 mmol) was dissolved in acetic acid (200 ml), and chlorine was bubbled through the stirred solution at room temperature for 4 h. The solution was set aside overnight; the ccd-dichloro-azine (111), separated as pale yellow crystals from the cool solution; recrystallisation from acetic acid yielded pure (111) (9.42 g, 34 mmol, 68%) m.p. 121-122" (1it.,l6 123") (Found: C, 60.55; H, 3.75; C1, 25.2. Calc. for C14H,,C1,N,: C, 60.6; Pre$avation of Benzaldehyde Axine TetYaZwomide.- Bromine (20 g, 250 mmol) was added during 2-5 h to benz- aldehyde azine (10.4 g, 50 mmol) dissolved in AnalaR carbon tetrachloride (600 ml) and cooled in ice-salt. An orange mass precipitated, and this was filtered off, washed free of excess of bromine with carbon tetrachloride; the product corresponded to the tetrabromide reported by Curtius (ref ., 16). The tetrabromide (m.p. 133'; yield 20.12 g, 38 mmol, 76%), gave satisfactory microanalysis, although the bromine was somewhat low, a feature often encountered in materials of this type (Found: C, 31-2; H, 2.45; Br, 59-6; N, 5.4. Calc. forCl,Hl,Br,N2: C, 31.2; H, 2-25; Br, 60.5; N, 5.3%). Its iodometric analysis was 1-37 active bromine per molecule of tetrabromide. Its i.r. spectrum showed the C=N (stretch) frequency at 1660 cm-l, and its 1H n.m.r. spectrum (in carbon tetrachloride) had a peak at T 0.59, both of these spectral features indicating the presence of C=N+ in the molecule. The azine could be recovered (93%) from the tetrabromide, by the method described above for the per- bromides. H, 3.65; C1, 25.6%). A State Maintenance Allowance for Research, held by P. A. C., is gratefully acknowledged. [0/1006 Received, June 15th, 19701
ISSN:0022-4952
DOI:10.1039/J39700002674
出版商:RSC
年代:1970
数据来源: RSC