The tautomerism of eight benzofuroxans has been studied by proton magnetic resonance a t low temperatures. Theequilibrium constants implied small (0-500 cal./mole) energy differences, and indicated that electron-acceptor groups favoured the 6-position and electron-donor groups the 5-position. The activation energies for the equilibrations were in the region of 14 kcal./mole. NUCLEAR MAGNETIC RESONANCE spectroscopy has established the structure of benzofuroxan as a rapidlyequilibrating system between benzofurazan 1-and 3oxides (I + 11; R = H), probably via the intermediate o-dinitrosobenzene (111) .2-6 The activation energy (estimated at ca. 15 kcal./mole3) for the equilibration is such that the aromatic protons show coalescence temperatures near 5" , averaging chemical shifts of ca. 8 ~. / s e c .~ 4-Nitrobenzofuroxan shows a single ABC spectrum a t all temperatures, indicating that one form, presumably represented by formula (IV; R = NO,), predominates to the extent that the alternative 3-oxide structure is undetectable at the low temperatures required to " freeze " the equilibrium on the n.m.r. time-scale. In the case of the corresponding 5-substituted derivative, however, both 5-nitro-(I) and 6nitro-(11; R = NO,) structures are present, the spectrum a t -31" indicating that ca. 70% of (11) exists with ca. 30% of (I) in the equilibrium r n i x t~r e .~ Other benzofuroxans which have been studied by n.m.r. at low temperatures include the 5,6-dinitr0-,~~7,8 5,6-di-~h l o r o -,~ 4,7-dichloro-,9 4,7-dibromo-,79 and &methyl-7 compounds. ?- RThe equilibrium between (I) and (11) appears to provide a direct comparison between the electronic properties of the nitrogen atom (position 3) and the N-oxide group (position 1) of the benzofuroxan system. At first sight, it might be supposed that both electron-5 G. Englert, 2. anulyt.
No abstract
Two dimers of cyclohexanethione are shown by proton resonance spectroscopy to be 2,2 :4,4-bispentamethylene-1,3-dithietan, and Z12-pentamethylene-4,5-tetrarnethylene-l,S-dithiolan. The latter was shown to be the cis-isomer by independent synthesis of the trans-analogue.THIOACETONE dimer was mentioned by Wislicenus before thioacetone itself had been characterised. This dimer, postulated and later investigated by many and its analogues, the dimers of methyl ethyl,* diethyl,8 and di-n-propyl thioketone, were arbitrarily assigned 1,3-&thiacyclobutane structures(1).Bohme, Pfeifer, and Schneider lo were unable to confirm the existence of 2,2,4,4-tetramethyl-l,3-dithietan (I; R1 = R2 = R3 = R4 = Me). However, they proposed the bicyclic dithietan structure (11) for the reaction product of chloroacetone and hydrogen sulphide (cf. also refs. 11, 12). Hromatka and Engel l3 rejected the dithietan formulation (11) for this compound in favour of 2,5-dimethyl-2,5-endosulphido-1,4-dithian (111).
Hz, C2-H and C6-H, respectively ), 4.62 (2 H singlet, -CH20-), 3.14 and 2.97 (10 H, unresolved singlets, OH, NH, and (CH2N)4). There was no CHa signal. The mixture melting points with samples prepared by the other routes showed no depression. The ir spectra of these samples were essentially superimposable.Microbiological Oxidation of N-(3-Chloro-4-methylpheny 1 )-N',N'-diethylethylenediamine Hydrochloride (III).-Essentially the same procedure was used here. A total of 161 g (0.58 mole) of substrate was converted over an 8-day period. The substance, was extracted and concentrated as in the above procedure.However, tie examination of the residue indicated that there was a minor component which furnished a positive test with 2,4-DNP. Accordingly, the residual oil was dissolved in 21)0 ml of methanol and treated with 6.0 g of NaBH4. After 30 min this carbonyl-positive component had disappeared as judged from tic. The methanol was removed and the residue was dissolved in 500 ml of CHC13. The solution was washed several times with water and concentrated to a small volume. On cooling the crystals were filtered and washed with hexane. There was obtained 93 g of IV as white crystals, mp 66.0-67.5°(Tor). The filtrate yielded an additional 13.5 g, making the total yield 106.5 g (0.385 molei or 66% of the theoretical. This was identical IR,. mixture melting point, and ir spectra) with the sample prepared chemically.
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