Primary RSSs

Weakly basic anion resins derive their functionality from primary (R-NH), secondary (R-NHR ), tertiary (R-N-R 2), and sometimes quaternary amine groups. The weakly basic resin readily absorbs such free mineral acids as hydrochloric and sulfuric, and the reactions may be represented according to the following ... 

With primary R, the reaction probably goes through the alkyl halide formed initially in an Sn2 reaction ... 

Primary (R = H) and secondary aromatic amines react with alkenes in the presence of thallium(III) acetate to give vie- diamines in good yields. " The reaction is not successful for primary aliphatic amines. In another procedure, alkenes can be diaminated by treatment with the osmium compounds R2NOSO2 and R3NOSO (R = t-Bu)," analogous to the osmium compound mentioned at 15-51. The palladium-promoted method of 15-51 has also been extended to diamination. " Alkenes can also be diaminated indirectly by treatment of the aminomercurial compound mentioned in 15-51 with a primary or secondary aromatic amine. 

The experimental enthalpies of protonation and the formal enthalpies of protonation, RMgBr —RH, are fairly constant for structurally similar species (R = cycloalkyl, primary alkyl) and would be expected to be constant also for the primary cycloalkyhnethyl-magnesium bromides. For the two examples just discussed, the formal enthalpies of protonation that are calculated using the derived enthalpies of formation for the cyclopropyl-and cyclobutylmethyhnagnesium bromides are 262 and 235 kJmoU, respectively. The mean value is thus 248 kJmoU, which is very close to that expected for the formal protonation of other primary R groups. 

The reaction can be extended to ot,ot-dihalo esters1557 and a,a-dihalo nitriles.1558 It is possible to replace just one halogen or both. In the latter case the two alkyl groups can be the same or different. When dialkylation is applied to dihalo nitriles, the two alkyl groups can be primary or secondary, but with dihalo esters, dialkylation is limited to primary R. Another extension is the reaction of boranes with -y-halo-a.p-unsaturated esters.1559 Alkylation takes place in the -y position, but the double bond migrates, e.g.,... 

Secondary R groups are harder to cleave, and primary R harder still. Because of this reaction, care must be taken when using Friedel-Crafts catalysts (Lewis or proton acids) on aromatic compounds containing alkyl groups. True cleavage, in which the R becomes an olefin, occurs only at high temperatures—above 400°C.425 At ordinary temperatures, the R group attacks... 

The rates of SN1 reactions of simple alkyl derivatives follow the order tertiary R secondary R primary R, which is exactly opposite that of SN2 reactions. This is evident from the data in Table 8-2, which lists the relative rates of hydrolysis of some alkyl bromides only the secondary and tertiary bromides react at measurable rates, and the tertiary bromide reacts some 105 times faster than the secondary bromide. 

As for the alkyl group, there are two important structural effects to notice. First, at least one C-H bond adjacent (/3) to the leaving group is required. Second, the ease of E2 elimination follows the order tertiary R > secondary R > primary R. Unlike SN2 reactions, which are not observed for tertiary alkyl compounds because of steric hindrance to the approach of the nucleophile to carbon, the related E2 reaction usually occurs readily with tertiary RX compounds. The reason is that little or no steric hindrance is likely... 

Factors influencing the El reactions are expected to be similar to those for the SN1 reactions. An ionizing solvent is necessary, and for easy reaction the RX compound must have a good leaving group and form a relatively stable R cation. Therefore the El orders of reaction rates are X = I>Br>Cl>F and tertiary R > secondary R > primary R. 

Another practical limitation of esterification reactions is steric hindrance. If either the acid or the alcohol participants possesses highly branched groups, the positions of equilibrium are less favorable and the rates of esterification are slow. In general, the ease of esterification for alcohols, ROH, by the mechanism described is primary R > secondary R > tertiary R with a given carboxylic acid. 

Primary (R CH2 N02), and also secondary (R2CH-N02), nitroalkanes exist in tautomeric equilibrium with the corresponding nitronic acids, the two species being interconvertible via the mesomerically stabilised a-carbanion. These nitroalkanes are therefore soluble in alkali. 

SHondary C H btmd 401 kJ/mo) 196 kcal/ mol)l, which h in turn wcatff than a piiinai C-H bond 1420 kJ/md (100 kcaVmol>]- Since leiw energy is needed to break a tertiary C-H bond than to break a primary or aecondaiy C-H bond, the resvJtanc tertiaiy radical ta more stable than a primary r secandaiy radical. 

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