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Because of steric hindrance to attack at the functional silicon centre in VsiSiMe2OCOR [where Vsi denotes (Me3Si)2(CH2CHMe2Si)C] with R = CF3(1a) or Me (1b), nucleophiles in MeOH can preferentially attack at the carbonyl group to give VsiSiMe2OH, rather than at Si as would be usual for less hindered silicon carboxylates. With CsF or KSCN in MeOH the products are exclusively VsiSiMe2F and VsiSiMe2NCS, respectively, whereas KOCN gives exclusively VsiSiMe2OH, and NaN3 gives very predominantly VsiSiMe2OH along with a little VsiSiMe2N3. The overall effectiveness of the salts is KOCN > CsF, NaN3 > KSCN; the sequence of the case of attack of the nucleophiles at Si is F– > SCN–(>N3–?), and that for attack at carbon is OCN– > N3– > F– > SCN–. The sequence of ability of various nucleophiles to catalyse cleavage of the SiO–COR bond of (1a) in MeOH is RNH2(R = H2N, Me, Et, HOCH2CH2, or H2NCH2CH2), OCN–, HO2– > MeO– > N3– > Me2NH > Me3N > 4-Me2NC5H4N C5H5N > PhNH2, and the sequence for reactions of the less reactive (1b) is HO2– > H2NNH2 > MeO– > H2NCH2CH2NH2 > MeNH2 > HOCH2CH2NH2 > EtNH2. Except for the unexpected effectiveness of OCN–, the sequences are reasonably consistent with those established, for example, for reactions of aryl acetates in water (and also with Ritchie's nucleophilic parameters N+); it is suggested that, as in the latter reactions, the cleavage of the acyl–oxygen bond is rate-determining. Reactions of (1a) with salts MX, namely NaN3, CsF, KSCN, and KOCN in MeCN, give exclusively the corresponding species VsiSiMe2X. In the representative reactions examined the reactivities of (1a) and (1b) were very similar to those of the corresponding compounds (Me3Si)3CSiMe2OCOR.

A simple method for the separation and determination of selenium(IV) and molybdenum(VI) in mixtures, based on selective precipitation with potassium thiocarbonate, has been developed. The procedure allows quantitative determination of 10-100 mg of selenium or 10-70 mg of molybdenum at pH 0.5-1.0. No interference by a wide range of other metal ions is observed.

Particles from compressed natural gas (CNG) engine emissions are smaller than those from diesel or even petrol engine emissions and range from 0.01-0.7 ~tm, with majority being between 0.020 and 0.060 p.m. (Ristovski et a12000). Very little data is available on particle emissions from CNG fuelled vehicles. An isolated study in this area by Greenwood et al (1996), indicated that the particle concentration levels emitted from CNG fuelled engines are similar to those from gasoline engines, and at high loads approach those of diesel engines. Recent studies conducted by Ristovski et al (2000) showed that the observed levels of particle emission were in terms of number of the same order as emissions from heavy-duty diesel engines. On the other hand emissions of CO and NOx for one of the tested engines, were considerably lower than the maximum allowed by the standards.