Hydrochloric acid nucleophilic addition reactions

Complexes 79 show several types of chemical reactions (87CCR229). Nucleophilic addition may proceed at the C2 and S atoms. In excess potassium cyanide, 79 (R = R = R" = R = H) forms mainly the allyl sulfide complex 82 (R = H, Nu = CN) (84JA2901). The reaction of sodium methylate, phenyl-, and 2-thienyllithium with 79 (R = R = r" = R = H) follows the same route. The fragment consisting of three coplanar carbon atoms is described as the allyl system over which the Tr-electron density is delocalized. The sulfur atom may participate in delocalization to some extent. Complex 82 (R = H, Nu = CN) may be proto-nated by hydrochloric acid to yield the product where the 2-cyanothiophene has been converted into 2,3-dihydro-2-cyanothiophene. The initial thiophene complex 79 (R = R = r" = R = H) reacts reversibly with tri-n-butylphosphine followed by the formation of 82 [R = H, Nu = P(n-Bu)3]. Less basic phosphines, such as methyldiphenylphosphine, add with much greater difficulty. The reaction of 79 (r2 = r3 = r4 = r5 = h) with the hydride anion [BH4, HFe(CO)4, HW(CO)J] followed by the formation of 82 (R = Nu, H) has also been studied in detail. When the hydride anion originates from HFe(CO)4, the process is complicated by the formation of side products 83 and 84. The 2-methylthiophene complex 79... 

A Sandmeyer reaction leading to the 3-chloro derivatives was observed upon treatment of 3-diazotriazoles with aqueous hydrochloric acid [1898LA33 26JCS1729 78ZN(B)216]. 3-Diazotriazole was reduced to the parent triazole by treatment at 0°C with primary and secondary alcohols [86DIS(B) (46) 3052]. The mechanism is not clear, but the process may be envisaged as involving hydride transfer from the intermediate 244 obtained by nucleophilic addition of alcohols to the diazo compound (Scheme 70). 

Upon heating the diarylthiourea with concentrated hydrochloric acid, it is partly converted into the aryl isothiocyanate (e.g. phenyl isothiocyanate or phenyl mustard oil, Expt 6.98, Method 1). A little hydrogen sulphide is evolved in a side reaction forming diphenylcarbodi-imide (4) which undergoes nucleophilic addition of aniline to yield triphenylguanidine (5), isolated from the reaction mixture as the hydrochloride. 

The hydrolysis rates of 1,3-dioxolanes are decreased by substitution of four methyl groups at the positions 4 and 5. 2,4,4,5,5-Pentamethyl-l,3-dioxolane reacts 6.5 times more slowly than 2-methy 1-1,3-dioxolane [161]. The AS value is decreased by 9 eu. A Hammett p value of—2.0 has been found for the substituent effect on the hydrolysis of 2-phenyl-4,4,5,5-tetramethyl-l,3-dioxolane in dilute aqueous hydrochloric acid [167]. The data obey the simple Hammett equation, and it is not necessary to apply o+ values. For the reaction of the unsubstituted 2-phenyl-4,4,5,5-tetramethyl compound, the solvent isotope effect is kH/kD = 0.42, and AS is —14.2 eu. General catalysis by formic acid has been observed in the hydrolysis of the p-methoxy compound. However, the rate is not significantly increased by addition of strong nucleophiles. 

Protonation of the 1,2,4-triazine ring enhances its electrophilicity and, therefore, facilitates the addition of carbanionic nucleophiles. However, only a limited number of C-nucleophiles may be used in reactions with yv//-triazinium substrates, because of possible proton transfer from substrate to reagent. Acetone seems to be an appropriate reagent for this kind of reaction, in spite of its very low C-nucleophilic character. Thus, 6-phenyl-1,2,4-triazin-3-one dissolved in acetone in the presence of hydrochloric acid gives the C-5 adduct 21 (Scheme 16) (85ACS(B)235). It is of interest that 5-phenyl-1,2,4-triazin-3-one remains unreactive under identical conditions, indicating that the addition reaction is sensitive to steric effects and can be completely blocked when the most reactive C-5 position carries a substituent. 

The condensation of formaldehyde and olefins is of industrial interest. Generally anti addition of the oxonium ion and nucleophile to the double bond predominates. The reaction of (E)-butene with formaldehyde in the presence of hydrochloric acid gives a mixture of anlijsyn (85 15) products. 

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