Secondary alkyl halide

This is not a new reaction. This is just an Sn2 reaction. We are simply using the alkoxide ion (ethoxide in this case) to function as the attacking nucleophile. But notice the net result of this reaction we have combined an alcohol and an alkyl halide to form an ether. This process has a special name. It is called the Williamson Ether Synthesis. This process relies on an Sn2 reaction as the main step, and therefore, we must be careful to obey the restrictions of Sn2 reactions. It is best to use a primary alkyl halide. Secondary alkyl halides cannot be used because elimination will predominate over substitution (as seen in Sections 10.9), and tertiary alkyl halides certainly cannot be used. 

RDX, Cyclonite, Hexahydro-l,3,5-trinitro-l,3,5-triazine under Secondary Aliphatic Amines Ring-Substituted Aromatics Saturated Alkyl Halides Secondary Alcohols... 

Primary alkyl halide Secondary alkyl halide Tertiary alkyl halide... 

Relative to tertiary alkyl halides, secondary derivatives react considerably slower. At room temperature and long reaction periods ( 24h) cyclohexyl chloride is almost quantitatively methylated with dimethyltitanium dichloride (prepared in situ from dimethylzinc and catalytic amounts of TiQ4)137>, but other cyclic or acyclic halides tend to undergo competing rearrangements prior to C—C bond formation 77). The same applies to 1,2-dihalides such as 1,2-dibromocyclohexane which affords 1,1-dimethylcyclohexane instead of the 1,2-dimethyl derivative137. In complete contrast, activated secondary chlorides behave much like tertiary derivatives, i.e., methylation is fast and position specific at low temperatures. Examples are shown in Equation 86137>. It should be noted that in such cases cuprate chemistry affords less than 40 % of methylation products138). 

H Hydrocarbon 1 H Alkyl halide, Secondary 1 H Secondary alcohol... 

Problem 6.20 Assuming the choice to be limited to alkane, alkene, alkyl halide, secondary alcohol, and tertiary alcohol, characterize compounds A, B, C, D, and E on the basis of the following information ... 

One of the two hydrogen atoms of phosphoramidates can be temporarily blocked with a trimethylsilyl group. The sodium salt of diethyl V-(trimethylsilyl)phosphoramidate (102) reacted with alkyl bromides in benzene in the presence of 10 mol % of tetra-n-butylammonium bromide to afford, after desilylation, the corresponding V-alkyl derivatives (103) in 79-95% yields for primary alkyl halides. Secondary alkyl halides gave poor results (Scheme 43). The addition of the quaternary ammonium salt is essential to promote the alkylation reaction. Hexamethyldisilazane and its cyclic analogs can also be utilized in the preparation of amines under moderate conditions (Scheme 43). ... 

Deoxygenation.. Al (by adding an alkyl halide Secondary allylic alcoh EtjSiH-LiClO. The fa... 

If primary amines react with alkyl halides, secondary amines are produced. If the reactions are allowed to proceed, tertiary amines can be obtained. 

Alkyl halides. Secondary and tertiary alcohols react with the reagent to form aUcyl fluorides. If an alkali halide (NaF, NaCl, NH4Br, Kl) is added to the reaction, alkyl halides, even primary, are formed corresponding to the added salt. The displacement proceeds with inversion. 

The reactivity of alkyl halides follows the order tertiary alkyl halide > secondary > primary taking into considerations of alkyl group. 

Ethers are prepared using the Williamson ether synthesis, which is an 8 42 reaction between an alkoxide and a methyl or primary alkyl halide (secondary or tertiary allg l halides give too much imwanted E2 elimination). 

Ethers can be readily prepared from the reaction between an alkoxide ion and an alkyl halide, a process called a Williamson ether synthesis. This process works best for methyl or primary alkyl halides. Secondary alkyl halides are significantly less efficient, and tertiary alkyl halides cannot be used. 

As mentioned earlier, the allyl cation can be captured at either carbon sharing the positive charge. Table 12.3 gives some average rates of SnI solvolysis for a few common structural types. Primary allylic halides react much faster than primary alkyl halides. Secondary and tertiary allylic halides also ionize faster than their non-allylic counterparts. Resonance stabilization does have an accelerating effect on the ionizations. 

In the reaction of ammonia with the alkyl halide, secondary and tertiary amine formation become more important as the concentration of ammonia is reduced. In favourable cases, e.g. the mono-, di- and trioctylamines firom ammonolysis of n-octyl chloride , the amines may be separable by distillation. In other cases, chemical methods... 

Simple aldehyde, ketone, and ester enolates are relatively basic, and their alkylation is limited to methyl and primary alkyl halides secondary and tertiary alkyl halides undergo elimination. Even when alkylation is possible, other factors intervene that can reduce its effectiveness as a synthetic tool. It is not always possible to limit the reaction to monoalkylation, and aldol addition can compete with alkylation. With unsymmetrical ketones, regioselectivity becomes a consideration. We saw in Section 20.2 that a strong, hindered base such as lithium diisopropylamide (LDA) exhibits a preference for abstracting a proton from the less-substituted a carbon of 2-methylcyclohexanone to form the kinetic enolate. Even under these conditions, however, regioisomeric products are formed on alkylation with benzyl bromide. 

Table 9.4 summarizes the reactivity of alkyl halides in Sn2 and SnI reactions. Primary alkyl halides, secondary alkyl halides, and methyl halides undergo only Sn2 reactions because of their relatively unstable carbocations. All tertiary halides (alkyl, allylic, and benzylic) undergo only SnI reactions, because steric hindrance makes them unreactive in Sn2 reactions. Primary and secondary allylic and benzylic halides undergo both SnI and Sn2 reactions. Vinylic and aryl halides cannot undergo either SnI or Sn2 reactions. 

Primary alkyl halides, secondary alkyl halides, and methyl halides undergo only Sn2 reactions. 

We recall that the Williamson method works best with primary alkyl halides. Secondary and especially tertiary alkyl halides undergo elimination reactions rather than the S 2 reaction that gives the ether. The reaction may be carried out in protic solvents such ethyl alcohol or aprotic solvents such as acetone or dimethylformamide. 

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