Bromides primary

Bromide Primary alkyl- H H Sn2 transition state Primary Water... 

If we look at a commonly used nucleophilic substitution, the replacement of OH by Br, we find that two quite different reaction conditions are used. Tertiary alcohols react rapidly with HBr to give tertiary alkyl bromides. Primary alcohols, on the other hand, react only very slowly with HBr and are usually converted to primary alkyl bromides with PBr3. 

Isobutyl bromide primary, therefore less reactive in S 1... 

These complexes show high catalytic activity (0.5 mol% loading) in short reaction times for the aryl amination of aryl chlorides, triflates, and bromides. Primary and secondary amines, both alkyl and aryl, are well tolerated. The mirroring of results can be emphasized if these palladacycles are compared to the (NHC)Pd(allyl)Cl systems, supporting the idea of identical active species [NHC-Pd] during the catalytic cycle. One of the limitations of these catalytic procedures or catalysts is their hmited activity for the couphng of electron-rich heterocycles with aryl hahdes. 

A further extensive paper and two associated patents have revealed more of the interesting chemistry of bis(trifluoromethyl)thioketen. The reactions encompassed by these publications include additions of water, alcohols, thiols, hydrogen bromide, primary and secondary amines, NN-dimethylanilines, ethers, and silicon and tin hydrides (Scheme 30), as well as an extensive series of ene reactions (Scheme 31). 

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. 

Other alkylbenzenes may be prepared similarly by using the appropriate primary or secondary alkyl bromide. 

Primary bromides give a precipitate of sodium bromide within 3 minutes at 25° chlorides react only when heated at 50° for up to 6 minutes. Secondary and tertiary bromides must be heated at 50° for up to 6 minutes, but tertiary chlorides do not react within this time. 

In the first method a secondary acetylenic bromide is warmed in THF with an equivalent amount of copper(I) cyanide. We found that a small amount of anhydrous lithium bromide is necessary to effect solubilization of the copper cyanide. Primary acetylenic bromides, RCECCH Br, under these conditions afford mainly the acetylenic nitriles, RCsCCHjCsN (see Chapter VIII). The aqueous procedure for the allenic nitriles is more attractive, in our opinion, because only a catalytic amount of copper cyanide is required the reaction of the acetylenic bromide with the KClV.CuCN complex is faster than the reaction with KCN. Excellent yields of allenic nitriles can be obtained if the potassium cyanide is added at a moderate rate during the reaction. Excess of KCN has to be avoided, as it causes resinifi-cation of the allenic nitrile. In the case of propargyl bromide 1,1-substitution may also occur, but the propargyl cyanide immediately isomerizes under the influence of the potassium cyanide. 

Note 2. Propargyl bromide itself also reacts with ammonia and therefore the interval between the addition of this compound and its conversion with the enethiolate should be kept as short as possible. Inverse addition was applied if propargyl bromide is added to the enthiolate solution, the primary product partly isomerizes into H2C=C(5C2Hs)SCH=C=CH2 under the catalytic influence of the enethiolate. 

Carbonylation of halides in the presence of primary and secondary amines at I atm affords amides[351j. The intramolecular carbonylation of an aryl bromide which has amino group affords a lactam and has been used for the synthesis of the isoquinoline alkaloid 498(352], The naturally occurring seven-membered lactam 499 (tomaymycin, neothramycin) is prepared by this method(353]. The a-methylene-d-lactam 500 is formed by the intramolecular carbonylation of 2-bromo-3-alkylamino-l-propene(354]. 

The major difference between the two mechanisms is the second step The second step m the reaction of tert butyl alcohol with hydrogen chloride is the ummolecular dis sociation of tert butyloxonium ion to tert butyl cation and water Heptyloxonium ion however instead of dissociating to an unstable primary carbocation reacts differently It IS attacked by bromide ion which acts as a nucleophile We can represent the transition state for this step as... 

Bromide ion forms a bond to the primary carbon by pushing off a water molecule This step IS bimolecular because it involves both bromide and heptyloxonium ion Step 2 IS slower than the proton transfer m step 1 so it is rate determining Using Ingold s ter mmology we classify nucleophilic substitutions that have a bimolecular rate determining step by the mechanistic symbol Sn2... 

A secondary alkyl radical is more stable than a primary radical Bromine therefore adds to C 1 of 1 butene faster than it adds to C 2 Once the bromine atom has added to the double bond the regioselectivity of addition is set The alkyl radical then abstracts a hydrogen atom from hydrogen bromide to give the alkyl bromide product as shown m... 

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... 

There are very large differences m the rates at which the various kinds of alkyl halides— methyl primary secondary or tertiary—undergo nucleophilic substitution As Table 8 2 shows for the reaction of a series of alkyl bromides... 

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

Primary carbocations are so high m energy that their intermediacy m nucleophilic substitution reactions is unlikely When ethyl bromide undergoes hydrolysis m aqueous formic acid substitution probably takes place by an 8 2 like process m which water is the nucleophile... 

Unbranched primary alcohols and tertiary alcohols tend to react with hydrogen halides without rearrangement The alkyloxonmm ions from primary alcohols react rap idly with bromide ion for example m an Sn2 process Tertiary alcohols give tertiary alkyl halides because tertiary carbocations are stable and show little tendency to rearrange... 

The secondary carbon bears more of the positive charge than does the primary carbon and attack by the nucleophilic bromide ion is faster there Hence the major product is the secondary bromide... 

The alkyl halide can be primary secondary or tertiary Alkyl iodides are the most reac tive followed by bromides then chlorides Fluorides are relatively unreactive... 

Sandmeyer reaction using cop per(l) bromide is applicable to the conversion of primary arylamines to aryl bromides... 

Diazotization of a primary arylamine followed by treatment of the diazo mum salt with copper(l) bromide or copper(l) chloride yields the corre spending aryl bromide or aryl chloride... 

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