Hydrogen chloride zinc reaction with dissolved form

If nitration under acidic conditions could only be used for the nitration of the weakest of amine bases its use for the synthesis of secondary nitramines would be severely limited. An important discovery by Wright and co-workers " found that the nitrations of the more basic amines are strongly catalyzed by chloride ion. This is explained by the fact that chloride ion, in the form of anhydrous zinc chloride, the hydrochloride salt of the amine, or dissolved gaseous hydrogen chloride, is a source of electropositive chlorine under the oxidizing conditions of nitration and this can react with the free amine to form an intermediate chloramine. The corresponding chloramines are readily nitrated with the loss of electropositive chlorine and the formation of the secondary nitramine in a catalytic cycle (Equations 5.2, 5.3 and 5.4). The mechanism of this reaction is proposed to involve chlorine acetate as the source of electropositive chlorine but other species may play a role. The success of the reaction appears to be due to the chloramines being weaker bases than the parent amines. 

Clement and Riviere [59] also reported that cellulose acetate or a mixed ester — a nitrate-acetate — can be obtained by reacting cellulose nitrate with acetic anhydride, acetic acid, and sulphuric acid. According to more recent contributions, e.g. Wolfrom, Bower and Maker [60], the reaction should be performed as follows Cellulose nitrate is dissolved in the cold in a little sulphuric add and acetic anhydride, the surplus of acetic anhydride is then hydrolysed also in the cold, and cellulose acetate is extracted with a suitable solvent, such as chloroform. Other methods of acetylating nitrocellulose consist in reduction, for instance with zinc and hydrogen chloride, which entails denitration of the ester, followed by acetylation with acetic anhydride. All these reactions are carried out in the same vessel. Further, it is possible to synthesize mixed esters, cellulose nitrate-acetates, by subjecting cellulose to the action of a mixture that includes nitric acid, acetic add and acetic anhydride in the presence of sulphuric acid (Kruger [61]). The use of a large amount of nitric acid favours the formation of nitrocellulose only. Mixed esters are formed... 

Dihydroxybenzaldehyde 5 9 0 A reaction flask (500-ml capacity) is fitted with an efficient stirrer, a reflux condenser, and a wide gas-inlet tube the end of the condenser is connected to, successively, a wash-bottle containing sulfuric acid, an empty safety flask, and a tube that passes over the surface of a sodium hydroxide solution. Resorcinol (20 g) and anhydrous ether (150-200 ml) are placed in the reaction flask, and anhydrous zinc cyanide (1.5 equivalents) is added. Then a rapid stream of dry gaseous hydrogen chloride is passed in. The zinc cyanide disappears as a milky mixture is formed and as the hydrogen chloride dissolves, the imide hydrochloride condensation product separates as a thick oil which solidifies in 10-30 min. The ether is usually saturated in 1.5 h, after which hydrogen chloride is passed in slowly for a further 0.5 h. Then the ether is decanted, water (100 ml) is added to the imide hydrochloride, and the solution is heated to the boiling point, filtered and allowed to cool. About half the aldehyde separates. After this has been collected the remainder of the aldehyde crystallizes in 10-15 h. The total yield is about 95 %, and the m.p. is 135-136° after recrystallization with charcoal from water. 

Hydrochloric acid is a strong monobasic acid, dissolving metals to form salt and evolving hydrogen. The reaction may be slow if the chloride formed is insoluble (for example lead and silver are attacked very slowly). The rate of attack on a metal also depends on concentration thus aluminium is attacked most rapidly by 9 M hydrochloric acid, while with other metals such as zinc or iron, more dilute acid is best. 

A recently described approach involving zinc dust for eliminating acid allows acylation by 9-fluorenylmethoxycarbonyl chloride without dimer formation. The amino acid is dissolved in acetonitrile with the aid of hydrochloric acid, and zinc dust is added to destroy the acid and deprotonate the zwitter-ion, reducing the protons to gaseous hydrogen (Figure 3.16). Acylation is effected in the presence of zinc dust, which reduces the proton that is liberated by the reaction as soon it is formed. See Section 7.7 for another possible impurity in Fmoc amino acids.34,36-39... 

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