Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Side reactions in reductions

Saturated Ketones and Ketol Acetates. Reductive Alkylation / 27 Mechanism of reduction / 27 Stereochemistry of reduction / 34 Side reactions in reductions / 37... [Pg.267]

C. Side Reactions in Reductions 1. Over-Reduction to Alcohol... [Pg.290]

Use of the trapping agent is recommended as the most efficient method for running acyloin condensations for many reasons. Among them are (a) the work-up is very simple filter and distil (b) the bis-(silyloxy)olefin is usually easier to store than the free acyloin and is readily purified by redistillation (c) unwanted base-catalyzed side reactions during reduction are completely avoided and (d) the bis-(silyloxy)olefin can be easily converted directly into the diketone by treatment with 1 mole of bromine in carbon tetrachloride.Other reactions are described in Riihlmann s review and in Organic Reactions ... [Pg.7]

There are ample precedents for reductions of double bonds in conjugated enones with lithium in deuterioammonia (see section V-C). Examples of the reduction of saturated ketones in deuterated media appear only as side reactions (over reductions) during the above mentioned conversions. For experimental details, therefore, one should consult the literature for the analogous reductions in protic medium (see also chapter 1). The use of deuterioammonia is essential for labeling purposes since by using liquid ammonia and methanol-OD the resulting alcohol contains no deuterium. For the preparation of deuterioammonia see section IX-D. [Pg.165]

The formation of vinylboranes and vinylboronate esters during some metal-promoted hydroboration of alkenes has led to the suggestion of an alternative mechanistic pathway. Insertion of the alkene into the metal-boron bond occurs in preference to insertion into the metal-hydride bond.44,51,52 In a competing side-reaction to reductive elimination, f3-H elimination from the resulting borylalkyl intermediate furnishes the vinylborane byproduct.52 There remains however a substantial body of evidence, both experimental53 and theoretical,54 that supports the idea that transfer of hydride to the coordinated alkene precedes transfer of the boryl fragment. [Pg.842]

The conditions of the FAB process also promote unwanted reactions between analyte and matrix. Even though such processes are not relevant in the majority of FAB measurements, one should be aware of them Besides addition or condensation reactions with matrix fragment ions, [81,82] reduction [83-86] and dehalo-genation [87,88] of the analyte represent the more prominent side-reactions in FAB. Electron transfer to cause the reduction of otherwise doubly charged ions have also been observed. [47]... [Pg.389]

The third method makes use of the one-flask procedure, which is advantageous from the preparative point of view. However, opening of certain stereoisomeric epoxides (263) with selenophenol suffers from low regioselectivity, resulting in a low yield of the final product. The other disadvantage is the basic reaction-medium occasioned by the method used for the generation of selenophenol, namely reduction of diphenyl diselenide with sodium borohydride in solution in anhydrous alcohol (see Ref. 356) some epoxides are sensitive to basic media. However, David (see Ref. 356) did not observe side reactions in his syntheses of 256. [Pg.53]

The tributyltin hydride reduction usually proceeds without complications. The most common byproduct is starting alcohol, which is postulated to be derived from a mixed thioacetal. Use of the phenyl thionocarbonate ester has been reported to minimize this side reaction in cases where it is a problem.6... [Pg.61]

Once again, it should be noted that the reductive condition in which the stoichiometric amount of chloro(pyridine)cobaloxime(III) was used, not only aided the addition of PCTFE to styrene, but also promoted the side reaction. In the IR spectrum of the resulting polymer, the reduction in the absorbance of the chloride band at 972 cm-i seemed to be too large, and the incorporation of oxygen in 3300 - 3600 cm-i region was also evident. The situation similar to the case of allyltributyltin might be applied in that THF possibly also took part in the reaction. [Pg.141]

In the case of the electron poor alkenes, results were more varied. Under all conditions examined, reactions with methyl vinyl ketone, acrylonitrile, methacrylonitrile and 4-vinyl pyridine afforded products with IR spectra equivalent to those obtained without the addition of the alkene (side reaction). In the cases of vinyl bromide and chloromethyl styrene, unreacted PCTFE was recovered unchanged. It is speculated that electron transfer to the alkene proceeded in each case. While the product of vinyl bromide reduction was not observed, perhaps because of volatility, one could isolate poly(chloromethylstyrene) in the latter case. [Pg.142]

The tin hydride method suffers from one major disadvantage, namely the efficiency of the reagent as a hydrogen atom donor. For successful synthesis, alkenes have to be reactive enough, otherwise direct reduction of the starting precursor becomes a considerable side reaction. In practice, the yields are increased by slow addition of a solution of tin hydride and a radical initiator into the reaction mixture containing an excess of alkene. However, a delicate balance must be maintained. If a large excess of olefin is used, polymerization can compete. 2,2-Azobisisobutyronitrile is the most commonly employed initiator, with a half-life time for unimolecular scission of 1 h at 80°C. [Pg.511]

In this context, it is worthwhile to mention that reduction of C=C bonds in a,(3-unsaturated carbonyl compounds can also occur as a side reaction in the reduction of... [Pg.79]

Most titanium(IV) alkyls tend to be reduced by aluminum alkyls in a complicated sequence of reactions accompanied by evolution of alkane and alkene. The catalytic activity of the bis(cyclopentadienyl)titanium-aluminum complexes is associated with the titanium alkyl. Hence, it is very interesting to investigate the mechanism of any reductive reaction. In order to study side reactions in the absence of polymerization, highly alkylated systems completely free of halogen are preferred. Moreover, reduction takes place much faster, the higher the alkyl-group content of the added aluminum alkyl. [Pg.132]

This reaction occurs to a greater extent in benzene than in isopropyl alcohol.13 27a It appears that an excess of aluminum iso propoxide has the desired effect of speeding up the reduction reaction and thus minimizing side reactions in the case of aliphatic aldehydes.13 The excess, however, is disadvantageous with aromatic aldehydes (see p. 195). [Pg.188]

Organometallics are formed at the cathode if transient radicals produced in reductions react with the active electrode. This occurs as a side reaction in cathodic coupling (Sect. 12.2, Eq. (185)) of carbonyl compounds, e.g., of acetone 3 9 or of activated olefins, e.g., of methyl vinyl ketone 41or acrylonitrile. Furthermore, in cathodic cleavage (Sect. 13.2, Eq. (227) ) of alkyl bromides or iodides organometallics are formed, e.g., ME(CH2CH2CN)2(ME = Pb, Tl, Sn, Hg) 481 bis(p-substituted benzyl)mercury 485 or dicyclopropylmercury 489 ... [Pg.164]

In aqueous reactions, it is also very important to follow the side reactions. In borohydride reductions, there is a side reaction with water ... [Pg.152]


See other pages where Side reactions in reductions is mentioned: [Pg.37]    [Pg.37]    [Pg.112]    [Pg.209]    [Pg.48]    [Pg.61]    [Pg.636]    [Pg.393]    [Pg.272]    [Pg.288]    [Pg.8]    [Pg.171]    [Pg.135]    [Pg.58]    [Pg.31]    [Pg.392]    [Pg.71]    [Pg.33]    [Pg.354]    [Pg.256]    [Pg.1362]    [Pg.132]    [Pg.757]    [Pg.112]    [Pg.121]    [Pg.244]    [Pg.748]    [Pg.256]    [Pg.240]   
See also in sourсe #XX -- [ Pg.37 ]

See also in sourсe #XX -- [ Pg.37 ]




SEARCH



© 2024 chempedia.info