Anti-Separation Additives

I. C. Callaghan and A. S. Taylor. Fluorosilicone anti-foam additive composition for use in crude oil separation. Patent GB 2234978,1991. 

Catalytic hydrosilylation of alkenes performed in the presence of a chiral catalyst results in the formation of chiral silanes. Initially platinium catalysts of the type L PtCl2, L = (/ )-benzyl-(methyl)phenylphosphine (BMPP) or (/ )-methyl(phenyl)propylphosphine and 1,1-disubstituted prostereogenic alkenes, such as a-methylstyrene, 2,3-dimethyl-l-butene and 2-methyl-l-butene, were used however, the stereoselectivity was low4,5. A slightly higher stereoselectivity is obtained when dichlorobis[(/ )-benzyl(methyl)phenylphosphine]nickel [Ni(BMPP)2Cl2] is used as the catalyst. Note that two chiral silanes are formed in this reaction, both of which are products of anti-Markovnikov addition. The major product is the expected dichlorosilane 3, while the byproduct is an anomalous chlorosilane 4 both products were separated by fractional distillation and the major product methylated to give the trimethylsilanes 56 7. 

Reaction of the a-carbanion of an alkyl aryl sulfoxide (RCH2SOAr) with aldehydes may give four dia-stereomers. In general, the reaction is highly diastereoselective with respect to the a-sulEnyl carbon, but poorly diastereofacially selective with respect to attack on the carbonyl component. In fact, the a-carb-anion (31) of benzyl t-butyl sulfoxide adds to an aldehyde to produce only two diastereomers (32a) and (32b). As shown in Scheme 10, the selectivity increases when the counterion is A transition state structure (33) is proposed to account for the anti stereoselection. Addition of the dianion of (/ )-3-(p-to-lylsulfinyOptopionic acid (34) to aldehydes affords two main diasteieoisomeric 3 (p-tolylsulfinyl)-y-lac-tones (35 R = Ph and Bu. ca. 60 40). These isomers (35) were separated by chromatography, and their... 

There is a broad range of additives for thermoplastics. Some of the more important additives include plasticizers, lubricants, anti-aging additives, colorants, flame retardants, blowing agents, cross-linking agents, and UV protectants. Fillers are also considered additives but are covered separately later. 

Miscellaneous Reactions. Hydwcyanation of olefins was among the very first reactions investigated in aqueous organic biphasic systems. [Ni(TPPTS)4] prepared separately or in situ from Ni(II) salts and TPPTS catalyze efficiently the anti-Markovnikov addition of HCN to butadiene and 3-pentenenitrile and also the isomerization of 2-methyl-3-butenenitrile to 3-pentenenitrile (Scheme 40). Lewis acid cocatalysts such as ZnCl2 facilitate the reaction. 

In a novel approach, an enantiomerically pure derivative of 2-amino-4,4,4- trifluorobutanoic acid was synthesized via nucleophilic trifluoromethylation (Figure 3) (5). In the key step. Gamer s aldehyde (2) (6), an oxazolidine derived from L-serine, reacted with the Ruppert-Prakash reagent, TMS-CF3 (a trifluoromethide equivalent) (7) and tetrabutylammonium fluoride. (S) - 5,5,5,5, 5, 5 - Hexafluoroleucine (3) (88% ee) was prepared in 18% overall yield from hexafluoroacetone and ethyl bromopyruvate in seven steps (8). The highly enantioselective reduction of the keto carbonyl group of 4 to the hydroxyester 5 either by baker s yeast and sucrose (91% ee) or by catecholborane and an oxazaborolidine catalyst (99% ee) was the pivotal reaction of the sequence. These workers (9) also prepared (-)-(R)- 4,4,4,4, 4, 4 -hexafluorovaline (6) (98% ee). The key step was the separation of the tosylate salts of the diastereomers formed by anti-Michael addition of (+)-(R)-... 

The four stage exhaust box Includes the oil box separator, the demister pad, the oil mist eliminator, and the synthetic oil baffle. Additional features include ein automotive type spin-on oil filter, a built-in inlet anti-suckback valve that prevents oil from being drawn into the system when the pump is stopped, eind a built-in gas ballast, available on the RA version, which permits pumping with high water vapor loads. 

Another class of configurationally stable a-mctallo amines is derived from the N-tert-butoxy-carbonyl-protected piperidines 32 and 3516, l7. Addition of the lithiated piperidines to aldehydes leads to mixtures of the anti- and. yin-diastereoiners. Although the diastereoselectivity is low, the diastereomers can be readily separated by chromatography since the. vyn-isomer is often in a cyclized form 34. The stereochemistry of the products obtained from piperidines 32 are consistent with an equatorial a-lithiation followed by addition to the aldehyde with retention of configuration. However, with piperidine 35 selective axial lithiation is observed. 

The unique feature of the Horner-Wittig reaction is that the addition intermediate can be isolated and purified, which provides a means for control of the reaction s stereochemistry. It is possible to separate the two diastereomeric adducts in order to prepare the pure alkenes. The elimination process is syn, so the stereochemistry of the alkene that is formed depends on the stereochemistry of the adduct. Usually the anti adduct is the major product, so it is the Z-alkene that is favored. The syn adduct is most easily obtained by reduction of (3-ketophosphine oxides.269... 

This synthesis is shown in Scheme 13.59. Two enantiomerically pure starting materials were brought together by a Wittig reaction in Step C. The aldol addition in Step D was diastereoselective for the anti configuration, but gave a 1 1 mixture with the 6S, 1R-diastereomer. The stereoisomers were separated after Step E-2. The macrolactonization (Step E-4) was accomplished by a mixed anhydride (see Section 3.4.1). The final epoxidation was done using 3-methyl-3-trifluoromethyl dioxirane. 

In molecules containing two cyclobutenes, addition of organic azides 26 yielded two adducts, e.g. reaction with 50 with benzyl azide 56 produced the cr-isomer 57a in which the (V-benzyl substituents were sy -aligned and the C2-isomer 57b in which they were anti-orientated (Scheme 7). The structure of syn-isomer 57a was confirmed by X-ray (Figure 2). The fact that both isomers yielded the same fns-aziridine 58 upon photolysis made separation of the individual triazoline isomers unnecessary. 

The first chiral a-oxygenated stannanes were prepared by Still59. Addition of Bu3SnLi to a-methy l-/J-phenylpropionaldehyde followed by MOMC1 led to a separable 1 1 mixture of syn and anti alkoxy stannanes (Scheme 26). Lithiation with n-BuLi and addition of acetone gave the respective adducts with overall retention of stereochemistry. Thus, it is implied that the intermediate a-alkoxy lithio derivatives retain their configuration. 

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