Deuterated benzene

Most of these values differ from those given in the original papers and which have been derived by the unjustifiable comparison of the benzene deuteration data with the dedeuteration data for the substituted compound this same error has been made elsewhere by these Russian workers (seep. 265). In some cases there is no alternative to this approximation and the data so derived is marked with an asterisk. Some of the values differ very markedly from those given in the original papers and which seem to the reviewer to have been obtained by methods which defy the laws of simple arithmetic. b E, - 15.8. 

The H/D exchange between D2 and benzene was found to have a rate exceeding that of benzene deuteration by several orders of magnitude. This result shows that exchange and hydrogenation reactions follow different reaction paths. The exchange parameters were also found to be independent of the overall alloy composition. 

Technological advances, i. e. cw pumped acousto-optically Q-switched Nd YAG lasers with repetition rates of up to 5 kHz combined with multichannel detection systems have increased the ease of obtaining hyper Raman signals. By making use of this advanced technology, hyper Raman spectra of benzene and pyridine could be obtained by Ned-dersen et al. (1989). Spectra from benzene, deuterated benzene and carbon tetrachloride have been obtained with high signal-to-noise ratios by Acker et al. (1989). As example, we show in Fig. 6.1-17 the hyper-Raman spectra of benzene and deuterated benzene. 

Figure 7 Hyper-Raman spectra of CeHeexcited with a Nd YAG laser (Aq = 1.064 nm) Q-switched at 1 kHz (A) and of CgDe in the lower spectrum with the laser Q-switched at 6 kHz (B). Reproduced by permission of Elsevier Science from Acker WP, Leach DH and Chang RK (1989) Stokes and anti-Stokes hyper Raman scattering from benzene, deuterated benzene, and carbon tetrachloride. Chemical Physics Letters 155 491-495.

Photolysis of Cp2TiAr2 in benzene solution yields titanocene and a variety of aryl products derived both intra- and intermolecularly (293—297). Dimethyl titan ocene photolyzed in hydrocarbons yields methane, but the hydrogen is derived from the other methyl group and from the cyclopentadienyl rings, as demonstrated by deuteration. Photolysis in the presence of diphenylacetylene yields the dimeric titanocycle (28) and a titanomethylation product [65090-11-1]. 

Radiolabeled folate provides a powerful tool for folate bioavaHabiUty studies in animals and for diagnostic procedures in humans. Deuteration at the 3- and 5-positions of the central benzene ring of foHc acid (31) was accompHshed by catalytic debromination (47,48) or acid-cataly2ed exchange reaction (49). Alternatively, deuterium-labeled fohc acid (32) was prepared by condensing pteroic acid with commercially available labeled glutamic acid (50). 

However, such an explanation was not convincing for other authors. Maeda and Kojima found that the irradiation of 2-phenylthiazole in ethanol at 80°C led to the same products described before but in a different ratio. Under the same reaction conditions, 5-phenylthiazole gave 4-phenylisothiazole, while 4-phenyl-thiazole was converted into 3-phenylisothiazole. The most important observation those authors made was that deuterium incorporation occurred when the reaction was carried out in benzene at 80°C in the presence of deuterium oxide. In fact, 2-phenylthiazole furnished deuterated 3-phenyl-4-deuteroisothiazole and... 

This last result bears also on the mode of conversion of the adduct to the final substitution product. As written in Eq. (10), a hydrogen atom is eliminated from the adduct, but it is more likely that it is abstracted from the adduct by a second radical. In dilute solutions of the radical-producing species, this second radical may be the adduct itself, as in Eq. (12) but when more concentrated solutions of dibenzoyl peroxide are employed, the hydrogen atom is removed by a benzoyloxy radical, for in the arylation of deuterated aromatic compounds the deuterium lost from the aromatic nucleus appears as deuterated benzoic acid, Eq. (13).The over-all reaction for the phenylation of benzene by dibenzoyl peroxide may therefore be written as in Eq, (14). 

A kinetic isotope effect, kH/kD = 1.4, has been observed in the bromination of 3-bromo-l,2,4,5-tetramethylbenzene and its 6-deuterated isomer by bromine in nitromethane at 30 °C, and this has been attributed to steric hindrance to the electrophile causing kLx to become significant relative to k 2 (see p. 8)268. A more extensive subsequent investigation304 of the isotope effects obtained for reaction in acetic acid and in nitromethane (in parentheses) revealed the following values mesitylene, 1.1 pentamethylbenzene 1.2 3-methoxy-1,2,4,5-tetramethyl-benzene 1.5 5-t-butyl-1,2,3-trimethylbenzene 1.6 (2.7) 3-bromo-1,2,4,5-tetra-methylbenzene 1.4 and for 1,3,5-tri-f-butylbenzene in acetic acid-dioxan, with silver ion catalyst, kH/kD = 3.6. All of these isotope effects are obtained with hindered compounds, and the larger the steric hindrance, the greater the isotope... 

Nesmeyanov et a/.545 used a mixture of ferrocene, deuterated trifluoroacetic acid and benzene in the molar ratios 1 2 20 in a preliminary investigation of the reactivity of ferrocene and its derivatives. At 25 °C, rate coefficients were 1,620 x 10-7 (ferrocene) and 19.3 xlO-7 (acetylferrocene). In a subsequent publication by Alikhanov and Shatenshtein543 these values were altered to 1,600 x 10-7 and 1.5 x 10 7, respectively, and a value of 0.77 x 10"7 added for 1,1-diacetylferrocene. Under the same conditions, toluene gave a value of 0.3 x 10-7 so that the activating effects of these compounds relative to benzene can be approximately determined. 

Nesmeyanov et a/.546 have also measured the effects of substituents in deuteration of ferrocene by deuterated trifluoroacetic acid in dichloromethane at 25 °C. Rate coefficients were measured for ferrocene and its derivative in a range of such acid mixtures, the composition of which was omitted, and in some cases the rate of exchange for ferrocene was calculated on the basis of a linear relationship between log and —H0. Results including the calculated knl values are given in Table 161. It should be noted that, in discussing those results, the authors quoted the incorrect partial rate factors for dedeuteration of toluene arising from the use of the incorrect data for benzene (see p. 199). This should be taken into account... 

Blackley548 measured the rates of deuteration of biphenylene, fluorene, tri-phenylene, and phenanthrene relative to o-xylene as 6.15 5.85 1.08 1.32, which is in very good agreement with the values of 8.80 7.00 - 1.14 which may be deduced from the detritiation data in Table 159, obtained using anhydrous trifluoroacetic acid. Aqueous trifluoroacetic acid (with the addition in some cases of benzene to assist solubility) was used by Rice550, who found that triptycene was 0.1 times as reactive per aromatic ring as o-xylene (cf. 0.13 derivable from Table 159) whereas the compound (XXXI) was 0.9 times as reactive as o-xylene. An exactly comparable measure is not available from Table 158, but dihydroanthracene (XXXII), which is similar, was 0.51 times as reactive as o-xylene and... 

A relative reactivity of ferrocene benzene of 105-106 has been quoted557 following a kinetic study of the deuteration of ferrocene in acetic acid-trifluoroacetic acid mixtures at 25 °C, but the value is entirely in error, being based on two faulty assumptions. The data are given in Table 166 and a linear plot of log Art versus —H0 was extrapolated to — H0 = 5.0, a rate coefficient of 1.3 x 10 1 being obtained. This was compared to the Gold and Satchell value for dedeuteration... 

Nesmeyanov et al.564 have measured the rates of deuteration of benzene and cyclopentadienylmanganese tricarbonyl by deuterated sulphuric acid-trifluoro-... 

A kinetic study of dedeuteration at 25 °C yield the following rate coefficients for [2H]-C6H4R578> 579 (R = )4-Me, 1,900 2-Me, 530 3-Me, 2.7 4-Ph, 1,400 2-Ph, 260 3-Ph, < 0.2 2,3-benzo(l position of naphthalene) 20,000-30,000 and 3,4-benzo (2 position of naphthalene) 500. Rather surprisingly, the rates of dedeuteration were little different from the rates of deuteration and it should be noted that quoted partial rate factors in this work were obtained by dividing these rates for dedeuteration at 25 °C by the rates of deuteration of benzene at 20 °C and errors of a factor of 2 or more may be introduced by this. 

Sodium ethoxide in deuterated ethanol was used in a study of the rate of deuteration of anisolechromium tricarbonyl at 100 °C, the first-order coefficient (2.65 x 10 5) being reported as only 3 times greater than that for benzene, cf anisole in the reaction with potassamide in liquid ammonia (Table 177)591a. 

There is one further piece of kinetic evidence which throws light on an aspect of the benzidine rearrangement mechanism, and this is comparison of the rates of reaction of ring-deuterated substrates with the normal H compounds. If the final proton-loss from the benzene rings is in any way rate-determining then substitution of D for H would result in a primary isotope effect with kD < kH. This aspect has been examined in detail42 for two substrates, hydrazobenzene itself where second-order acid dependence is found and l,l -hydrazonaphthalene where the acid dependence is first-order. The results are given in Tables 2 and 3. 

Reactions at Eqs. (12) and (13) are carried out in toluene solution. The yellow crystalline products are purified by recrystallization from pentane and stored in a dry atmosphere at —20 °C. Reaction at Eq. (14) takes place slowly at 20 °C in benzene. The sulfane product H2S is separated from the silylester side product by distillation together with the benzene solvent (in the case of n=2-4) or by phase separation (for n=4, 5). For certain preparative purposes the ester and the solvent may not interfere. If deuterated triflu-oroacetic acid is used in the reaction at Eq. (14) the fully deuterated sulfane is obtained [29]. 

Geometries, hyperfme structure, and relative stabilities of the different positional isomers of monodeuterated benzene cations have been studied theoretically by density functional theory, using the B3-LYP functional, and experimentally by ESR and ENDOR spectroscopy. A comparison between theoretical and experimental results at 30 K gives acceptable agreement, but further experiments on multiply deuterated species should improve the analysis by making the effects of deuteration larger. 

We have previously in a number of papers [1-5] investigated these effects ft -both the Jahn-Teller inactive molecule n-butane [1] and the Jahn-Teller active molecules ethane, cyclopropane, and cyclohexane [2-5]. The choice of systems was largely dictated by the availability of experimental results [5-8]. New experiments being performed on selectively deuterated benzene have motivated a closer theoretical study of this system, and a first presentation of these investigations is given in the present paper. 

Table 3 Vibrational Frequency Components in the High- and Low-Frequency regions (cm ) and Total ZPVE (kJ mol ) for the Non- and Mono-Deuterated Isomers of the Benzene Radical Cation.

There are some interesting aspects of the results which deserve additional study. A close scrutiny of Table 3 reveals that the difference in ZPVE between the two isomers of the mono-deuterated benzene cation does only to a very minor extent (0.5 cm ) stem from the C—H (C—D) stretching vibrations, as one would... 

Additional experimental studies on multiply deuterated benzene cations would give more information, by enlarging the effects on the ZPVE and also by introducing new structural features in the experimental spectra which can facilitate their interpretation. This would enable a more detailed and more accurate analysis, both theoretically and experimentally. Such experiments will hopefully be carried out in the near future. 

DMSO or other sulfoxides react with trimethylchlorosilanes (TCS) 14 or trimefhylsilyl bromide 16, via 789, to give the Sila-Pummerer product 1275. Rearrangement of 789 and further reaction with TCS 14 affords, with elimination of HMDSO 7 and via 1276 and 1277, methanesulfenyl chloride 1278, which is also accessible by chlorination of dimethyldisulfide, by treatment of DMSO with Me2SiCl2 48, with formation of silicon oil 56, or by reaction of DMSO with oxalyl chloride, whereupon CO and CO2 is evolved (cf also Section 8.2.2). On heating equimolar amounts of primary or secondary alcohols with DMSO and TCS 14 in benzene, formaldehyde acetals are formed in 76-96% yield [67]. Thus reaction of -butanol with DMSO and TCS 14 gives, via intermediate 1275 and the mixed acetal 1279, formaldehyde di-n-butyl acetal 1280 in 81% yield and methyl mercaptan (Scheme 8.26). Most importantly, use of DMSO-Dg furnishes acetals in which the 0,0 -methylene group is deuter-ated. Benzyl alcohol, however, affords, under these reaction conditions, 93% diben-zyl ether 1817 and no acetal [67]. 

Deuterium NMR has recently been used to study molecular motion of organic adsorbates on alumina (1.) and in framework aluminosilicates (2). The advantage of NMR is that the quadrupole interaction dominates the spectrum. This intramolecular interaction depends on the average ordering and dynamics of the individual molecules. In the present work we describe NMR measurements of deuterated benzene in (Na)X and (Cs,Na)X zeolite. 

The application of deuterated toluene in assessing anaerobic biodegradation (Fischer et al. 2006) has already been noted in Chapter 6, Part 1. A review (Lovley 1997) has summarized the various strategies and suggests that uncertainties, particularly in the bioremediation of benzene, can only be resolved by greater emphasis on field-oriented studies, and a better understanding of the reactions involved and the factors that limit the rates of degradation. 

NSE measurements at zero average contrast conditions on a symmetric diblock copolymer of H-PS and D-PS dissolved in an appropriate mixture of proto-nated and deuterated benzene are reported [171,172]. The measurements were performed at different concentrations c > c. For comparison, the interdiffusion of a corresponding blend of H-PS and D-PS homopolymers dissolved in deuterated benzene was studied, too [171]. Owing to the relatively low molecular masses, only the regime Q1/2 < 1 was accessible, and the internal modes could not be probed. 

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