Reduction, of alkyl halides

Alkyl halides produce alkanes when they are reacted with reducing agents, such as Zn, in dilute acid. 

So in the reaction below Zn is acting as a reducing agent and the halogen in the alkyl halide is replaced by the hydrogen from the dilute acid. 

When sodium salts of carboxylic acids are heated with NaOH, alkanes are 

R — COONa + NaOH sodium salt of a carboxylic acid 

Soda-lime is a white granular mixture of calcium hydroxide and sodium hydroxide. 

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Stabilization of intermediates by strong adsorption will frequently be a necessary precondition for synthesis. Thus, in the case of the Kolbe reaction, further oxidation of the radicals is prevented the formation of metal-carbon bonds in the reduction of alkyl halides (Fleischmann et al., 1971a Galli and Olivani, 1970) or oxidation of Grignard reagents (Fleischmann et al., 1972c) is shown by the isolation of organometallic... 

The tin hydrides find important applications as reducing agents. Many of their reactions (particularly the reduction of alkyl halides and the hydrostannation of simple alkenes and alkynes) arc known to proceed through RaSn- intermediates, and this aspect of their chemistry is referred to in Section II,G. 

Trialkyltin radicals are important intermediates in the reduction of alkyl halides, and in the hydrostannation of alkenes (1, 287). 

The process of ligand transfer to give CrCP is well-established in the case of Cr(II) reduction of alkyl halides. 

Castro CE, WC Kray (1963) The cleavage of bonds by low-valent transition metal ions. The homogeneous reduction of alkyl halides by chromous sulfate. J Am Chem Soc 85 2768-2773. 

Scheme 5.7 illustrates these and other applications of the hydride donors. Entries 1 and 2 are examples of reduction of alkyl halides, whereas Entry 3 shows removal of an aromatic halogen. Entries 4 to 6 are sulfonate displacements, with the last example using a copper hydride reagent. Entry 7 is an epoxide ring opening. Entries 8 and 9 illustrate the difference in ease of reduction of alkynes with and without hydroxy participation. 

In 1949 von Stackelberg and Stracke proposed a general mechanistic scheme for the electrochemical reduction of alkyl halides (Scheme I) 15>. It was suggested that the reduction is stepwise, proceeding via initial one-electron... 

The reaction is a reduction of alkyl halide zinc atoms transfer electrons to the carbon atom of the alkyl halide. 

This is the basic reaction of the commercial Nalco process. On the other hand, reduction of alkyl halides at the cathode is often described in general terms as ... 

Neither reaction excludes the other, nor are these the only routes possible. The oxidation of alkylanions on a metallic anode is likely. Other processes are more clearly indicated when, instead of Cd, Zn is used as a cathode. In the latter case, zinc alkyls R2Zn and RZnI are formed by cathodic reaction of RI. This allows an efficient preparation of R4M where M = Pb, Sn and R = propyl, butyl or pentyl39, in contrast to the cathodic reduction of alkyl halides which is practically limited to the methyl and ethyl groups. 

Although the tin hydride reductions of alkyl halides seem simple, one must be careful because these reactions occur by a free radical mechanism. This is important, because the carbon radical produced in the reaction can isomerize68,78 and one often obtains two different stereoisomers from the synthesis. Another problem is that chiral centres can be lost in tin hydride reductions when an optically active halide is reduced. One example of this is the reduction of benzyl-6-isocyanopenicillanate with tributyltin deuteride78 (Scheme 14). The amount of isomerization depends on the temperature, the concentration of the tin hydride and the presence of and /-substituents78-82. However, some authors have reported tin hydride reductions where no racemization was observed78. 

Darensbourg et al. have conducted extensive studies of the nucleophilic reactivity of a series of anionic metal carbonyl hydrides [24], which have been used for the reduction of alkyl halides [25], acyl chlorides [26], and ketones [27]. The... 

REDUCTION OF ALKYL HALIDES AND TOSYLATES WITH SODIUM CYANOBOROHYDRIDE IN HEXAMETHYL-PHOSPHORAMIDE (HMPA) A. 1-IODODECANE TO n—DECANE B. 1-DODECYL TOSYLATE TO n-DODECANE, 53, 107 REDUCTION OF KETONES BY USE OF TOSYLHYDRAZONE DERIVATIVES ANDROSTAN-17 0—OL, 52, 122 REDUCTIVE AMINATION WITH SO-... 

Two-Step Chemical Catalysis of the Reduction of Alkyl Halides by Low-Valent Cobalamins and Cobinamides... 

Fig. 5 Marcus plot of electron transfer reductions of alkyl halides, as contrasted with archetypal SN2 substitution processes (Finkelstein reactions, circled see Eberson,...

Other disulfones like (32) and (33) were studied (see Ref [6]). They exhibit surprisingly stable anion radicals (and even a stable dianion with (32)). Such charged species could be used as redox mediators, tiowever, reduction of alkyl halides RX by (33) did not permit the formation of alkylated products presumably because of the strong steric strain induced by alkylation of the corresponding carbon atoms in the cyclobutene ring. 

It is known that the [Ni(I)(OEiBC)] complex mediates electrocatalytic reductions of alkyl halides and methyl p-toluenesulfonate [305]. The nucleophilic-ity of the Ni(I) complex is comparable to that of the supernucleophile vitamin Bi2. Recently, the formation of... 

Vitamin B12 derivatives and their model compounds have recently been used as recyclable electrocatalysts for the reduction of alkyl halides since low-valent Co species are good nucleophiles toward organic substrates [367-369]. Examples of such elec-trocatalysts are the vitamin B12 derivatives aquocobalamin (230), dibromo[l-hydr-oxy-2,2,3,3,7,7,8,8,12,12,13,13,17,17,18,18-hexadecamethyl-10,20-diazaoctahydropor-phinato]cobalt(III) (231), and cobaloxim (232). The above Co(I) complexes can be... 

The pattern for reduction of alkyl halides by Ni(tmc) + (12) closely resembles that by Cr(15[ane]N4) + (13). This suggests a similar mechanism for both reductants. There is strong... 

The reaction of thiyl radicals with silicon hydrides (Reaction 3.18) is the key step of the so called polarity-reversal catalysis in the radical-chain reduction of alkyl halides as well as in the hydrosilylation of olefins using silane-thiol couple (see Sections 4.5 and 5.1) [33]. The reaction is strongly endothermic and reversible (Reaction —3.18). 

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