Primary alkyl bromides

Place a mixture of 0-5 g. of finely powdered thiourea, 0-5 g. of the alkyl halide and 5 ml. of alcohol in a test-tube or small flask equipped with a reflux condenser. Reflux the mixture for a j)eriod depending upon the nature of the halide primary alkyl bromides and iodides, 10-20 minutes (according to the molecular weight) secondary alkyl bromides or iodides, 2-3 hours alkyl chlorides, 3-5 hours polymethy lene dibromides or di-iodides, 20-50 minutes. Then add 0 5 g. of picric acid, boil until a clear solution is obtained, and cool. If no precipitate is obtained, add a few drops of water. RecrystaUise the resulting S-alkyl-iso-thiuronium picrate from alcohol. 

Compound A (C7Hi5Br) is not a primary alkyl bromide It yields a single alkene (compound B) on being heated with sodium ethoxide in ethanol Hydrogenation of compound B yields 2 4 dimethylpentane Identify compounds A and B... 

Effect of Chain Branching on Reactivity of Primary Alkyl Bromides Toward Substitution Under Sn2 Conditions ... 

Linear alpha-olefins are the source of the largest volume of ahphatic amine oxides. The olefin reacts with hydrogen bromide in the presence of peroxide catalyst, to yield primary alkyl bromide, which then reacts with dimethylamine to yield the corresponding alkyl dimethyl amine. Fatty alcohols and fatty acids are also used to produce amine oxides (Fig. 1). 

A considerable amount of hydrobromic acid is consumed in the manufacture of inorganic bromides, as well as in the synthesis of alkyl bromides from alcohols. The acid can also be used to hydrobrominate olefins (qv). The addition can take place by an ionic mechanism, usually in a polar solvent, according to Markownikoff s rule to yield a secondary alkyl bromide. Under the influence of a free-radical catalyst, in aprotic, nonpolar solvents, dry hydrogen bromide reacts with an a-olefin to produce a primary alkyl bromide as the predominant product. Primary alkyl bromides are useful in synthesizing other compounds and are 40—60 times as reactive as the corresponding chlorides (6). 

Given the molecular formula CgHnBr, construct a molecular model of the isomer that is a primary alkyl bromide yet relatively unreactive toward bimolecular nucleophilic substitution. 

Because primary alkyl bromides can be converted into the corresponding nitro compounds by the acdon of NaNO in DMSO, primary alkyl bromides are converted directly into the corresponding carboxylic acids by the reacdon v/ith an excess of sodium nitrite in acedc acid rEq. 6-16 / ... 

A new route to nitnle oxides based on the reacdon of primary alkyl bromides v/ith NaNOj n the presence of acedc acid, is also reported fEq. 6.35. This reacdon is used for the direct... 

The alkylation reaction is limited to the use of primary alkyl bromides and alkyl iodides because acetylide ions are sufficiently strong bases to cause dehydrohalogenation instead of substitution when they react with secondary and tertiary alkyl halides. For example, reaction of bromocyclohexane with propyne anion yields the elimination product cyclohexene rather than the substitution product 1-propynylcyclohexane. 

The favourable effect of steric demand was also confirmed by the experiments of Fu while studying the coupling of primary alkyl bromides. Good yields were achieved using lAd HCl, under mild conditions and in the presence of Cul [127]. The results can be further improved using bulkier ligands such as lAd (bisdiamantyl-substituted NHCs) [128] (Scheme 6.42). 

Dimethylsulfonium methylide reacts with reactive alkylating reagents such as allylic and benzylic bromides to give terminal alkenes. A similar reaction occurs with primary alkyl bromides in the presence of Lil. The reaction probably involves alkylation of the ylide, followed by elimination.289... 

As a result of the inductive and hyperconjugative effects it is to be expected that tertiary carbonium ions will be more stable than secondary carbonium ions, which in turn will be more stable than primary ions. The stabilization of the corresponding transition states for ionization should be in the same order, since the transition state will somewhat resemble the ion. Thus the first order rate constant for the solvolysis of tert-buty bromide in alkaline 80% aqueous ethanol at 55° is about 4000 times that of isopropyl bromide, while for ethyl and methyl bromides the first order contribution to the hydrolysis rate is imperceptible against the contribution from the bimolecular hydrolysis.217 Formic acid is such a good ionizing solvent that even primary alkyl bromides hydrolyze at a rate nearly independent of water concentration. The relative rates at 100° are tertiary butyl, 108 isopropyl, 44.7 ethyl, 1.71 and methyl, 1.00.218>212 One a-phenyl substituent is about as effective in accelerating the ionization as two a-alkyl groups.212 Thus the reactions of benzyl compounds, like those of secondary alkyl compounds, are of borderline mechanism, while benzhydryl compounds react by the unimolecular ionization mechanism. 

Preparation from activated Cb(O).1 An activated Cu, prepared by lithium naphthalenide reduction of CuIPBu3 (12,140), reacts with primary alkyl bromides at -50 to -78° to form alkylcopper reagents that undergo 1,4-addition to cyclo-hexenone in moderate to high yield. This conjugate addition is facilitated by ClSi(CH3)3 and a phosphine. 

HMPT catalysis.13 Sml2 alone can reduce primary alkyl bromides or iodides in high yield, but the reaction is slow even in refluxing THF. In the presence of HMPT ( 5 mole %), alkyl, aryl, and vinyl halides, and even alkyl chlorides, are reduced in almost quantitative yield at 25°, often in less than 1 hour. 

Cyclohexyl xanthate has been used as a model compound for mechanistic studies [43]. From laser flash photolysis experiments the absolute rate constant of the reaction with (TMS)3Si has been measured (see Table 4.3). From a competition experiment between cyclohexyl xanthate and -octyl bromide, xanthate was ca 2 times more reactive than the primary alkyl bromide instead of ca 50 as expected from the rate constants reported in Tables 4.1 and 4.3. This result suggests that the addition of silyl radical to thiocarbonyl moiety is reversible. The mechanism of xanthate reduction is depicted in Scheme 4.3 (TMS)3Si radicals, initially generated by small amounts of AIBN, attack the thiocarbonyl moiety to form in a reversible manner a radical intermediate that undergoes (3-scission to form alkyl radicals. Hydrogen abstraction from the silane gives the alkane and (TMS)3Si radical, thus completing the cycle of this chain reaction. 

Carbonylation procedures have been successfully used for C—C bond forming radical strategies. Alkyl halides could be carbonylated under moderate pressure of CO (15-30 atm) in benzene at 80 °C in the presence of (TMS)3SiH and AIBN [16], Reaction (7.8) shows the effect of the CO pressure on the carbonylation of a primary alkyl bromide. These radical chain reactions proceed by the addition of an alkyl radical onto carbon monoxide, which generates... 

Homologues of ethoxyacetylene can be obtained by reaction of the metallated ethynyl ether in liquid ammonia with primary alkyl bromides and iodides 167]. Because of their better solubiliiy, the lithium compounds are preferred over their sodium and potassium analogues, lithium ethoxyacetylide is generated from the readily accessible 2-bromovinyl ethyl ether and two equivalents of lithium amide. This starting compound is obtained as a mixture of the E-and Z-isomer. When this mixture is heated with powdered KOH, only the Z-isomer is converted into ethoxyethyne. Alkali amides are able to conven both isomers into ethoxyethyne and its alkali compounds. A possible explanation for this violation of the "rule of... 

The reaction can be applied to varions secondary and primary alkyl bromides (Table 8). 

Under these conditions, a broad range of polyfunctional alkyl iodides are converted to the corresponding organozinc halides in high yields . In the case of primary alkyl iodides, the insertion occurs at 40-50 °C whereas secondary alkyl iodides already react at 25-30°C. Secondary alkyl bromides also react under these conditions , but primary alkyl bromides are usually inert with this type of activation and much better results are obtained by using Rieke zinc L Thus, the reduction of zinc chloride with finely cut lithium and naphthalene produces within 1.5 h highly reactive zinc (Rieke zinc). 

Rather unexpectedly, the reaction product of alkenylzirconocene chlorides can be alkylated with primary alkyl bromides under the influence of a catalyst-solvent system consisting of 2.5% Pd(acac)2, 2 equiv. LiBr and 1 1 THF-NMP without any phosphine and NMI used above881 (Scheme 77). 

R1 = -Hex, t-Bu, , EtO, THP(OCH2)2 etc. R2Br = Primary alkyl bromides... 

SCHEME 77. Pd-catalyzed alkylation of alkenylzirconocene chlorides with primary alkyl bromides... 

This is the case for secondary and tertiary alkyl bromides. If the stability is high, however, as, for example, with primary alkyl bromides, the organo nickel(III) complex is further reduced to an alkyl nickel(II) complex which loses the alkyl group in form of the alkyl anion. An electroinactive Ni(II) species remains. The number of regenerative cycles is consequently low. The structure of the ligand also influences the lifetime of the alkyl nickel(ni) complex thus, a less stable complex is formed in the case of [A,A -ethylene-bis(salicylidene-irainato)]nickel(II) ([Ni(salen)]) as compared with (5,5,7,12,12,14-hexamethyl-l,4,8,ll-tetraazacyclo-tetradecane)nickel(II) ([Ni(teta)] ), and hence the former complex favors the radical pathway even with primary alkyl halides. 

Alkyl bromides.1 The reagent cleaves oxiranes of type of example I exclusively lo primary alkyl bromides. Four-membered cyclic ethers also react readily, but llvc-mcmbered cyclic ethers require long periods of reflux, li samples ... 

Formylation and acetylation of a primary alkyl bromide.2 Detailed directions are available for preparation of disodium tctracarbonylferratesesquidioxanate, Na2Fe(CO)4(dioxanc), 5 (1), and for use of the reagent for preparation of aldehydes and ketones from alkyl bromides. 

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