Ammonium salt, dehydration

Dehydration of the corresponding ammonium salt. Thus ammonium acetate on heating loses water giving acetamide. An excess of acetic acid is... 

By the dehydration of the ammonium salt of the corresponding acid by heat or by distillation, for example ... 

The formation of amides can be accompHshed by dehydration of the ammonium salts of sahcyhc acid. The more common method for amines is the reaction of the ester, acyl hahde, or anhydride with an amine or ammonia. Each step is fast and essentially irreversible. 

Amides react ia certain cases to form ammonium salts of sulfonated amides (22). For example, treatment with ben2amide yields ammonium A/-ben2oylsulfamate [83930-12-5] C H CONHSO NH, and treatment with ammonium sulfamate yields dianmioiiiumimidodisulfonate [13597-84-17, HN(S020NH 2 Ammonium sulfamate or sulfamic acid and ammonium carbonate dehydrate Hquid or soHd amides to nitriles (27). 

There are two serious problems associated with continuous tar distillation. Coal tar contains two types of components highly corrosive to ferrous metals. The ammonium salts, mainly ammonium chloride, associated with the entrained Hquor remain in the tar after dehydration, tend to dissociate with the production of hydrochloric acid and cause rapid deterioration of any part of the plant in which these vapors and steam are present above 240°C. Condensers on the dehydration column and fractionation columns are also attacked. This form of corrosion is controlled by the addition of alkaU (10% sodium carbonate solution or 40% caustic soda) to the cmde tar in an amount equivalent to the fixed ammonia content. 

Cobalt(II) hydroxide [1307-86-4], Co(OH)2, is a pink, rhombic crystalline material containing about 61% cobalt. It is insoluble in water, but dissolves in acids and ammonium salt solutions. The material is prepared by mixing a cobalt salt solution and a sodium hydroxide solution. Because of the tendency of the cobalt(II) to oxidize, antioxidants (qv) are generally added. Dehydration occurs above 150°C. The hydroxide is a common starting material for the preparation of cobalt compounds. It is also used in paints and Hthographic printing inks and as a catalyst (see Paint). 

Determination of the influence of crystal structure and reactant environment on deammination and dehydration processes is complicated by the several solid phase transformations that are a characteristic feature of many ammonium salts. Sublimation and/or melting may also occur. Deammination and dehydration steps are generally reversible. At high temperatures, however, particularly in the presence of a residual oxide... 

Kubasova [963] has reviewed the chemistry of the ammonium salts of polyphosphoric acids. Much interest in the field derives from the agricultural uses of these substances as fertilizers. Both NH3 and H20 tend to be eliminated simultaneously on heating, but dehydration alone may be achieved in an atmosphere of NH3 [963], e.g. 

Small amounts (<3.5%) of ammonium salts markedly accelerate [970] the dehydration of Na2HP04 12 H20 to Na2P207. This is attributed to an increase in the concentration of delocalized protons in the structure, as a consequence of the proton donor properties of NH4, and this promotes dehydration. 

Hajek et al. [173] have reported a detailed kinetic study of the solid phase decomposition of the ammonium salts of terephthalic and iso-phthalic acids in an inert-gas fluidized bed (373—473 K). Simultaneous release of both NH3 molecules occurred in the diammonium salts, without dehydration or amide formation. Reactant crystallites maintained their external shape and size during decomposition, the rate obeying the contracting volume equation [eqn. (7), n = 3]. For reaction at 423 K of material having particle sizes 0.25—0.40 mm, the rate coefficients for decompositions of diammonium terephthalate, monoammonium tere-phthalate and diammonium isophthalate were in the ratio 7.4 1.0 134 and values of E (in the same sequence) were 87,108 and 99 kJ mole-1. 

Figure 4.24 Two amine-containing molecules can be crosslinked by formaldehyde through formation of a quaternary ammonium salt with subsequent dehydration to an immonium cation intermediate. This active species then can react with a second amine compound to form stable secondary amine bonds.

Since, as has been described above, amides can be obtained by removal of water from the ammonium salts of acids, nitriles can be prepared directly from ammonium salts in one operation by heating them with a powerful dehydrating agent, e.g. ammonium acetate with P205 ... 

Concerning the nature of the acid sites on dehydrated alumina, the chemical evidence is more in favor of Lewis-type than of Bronsted-type acids. Trambouze and Perrin (343) estimated the content of Lewis acid sites by thermometric titration of a slurry in benzene with dioxane. The authors stated that Lew is acidity was not observed in boehmite and its dehydration products, only in the products obtained from hydrargillite. As mentioned earlier, Webb (339) found no indication of Bronsted acidity ammonia did not form ammonium salts. The quantity of ammonia chemisoi-bed per unit area in the range from 175° to 500° was not a function of the hydrogen content. After exten.sive dehydration, more ammonia was chemisorbed at 100 mm pressure, even at 500°, than corresponded to the hydrogen present (341b). 

Amidation. Reactions leading to the formation of amides R-C-NH2. Examples include the dehydration (water removal) of the ammonium salts... 

Nucleophilic attack only occurs upon heating the ammonium salt, resulting in overall dehydration of the salt. Consequently, it is usual to prepare amides by using a more favourable substrate than the carboxylic acid, one that is more reactive towards nucleophiles by virtue of possessing a better leaving group, and where salt formation does not hinder the reaction. 

C as shown in TPD curve of Fig. 2A. When S02 is evolved during the TPD experiment, there is neither absorbed nor released heat as shown in DTA curve of HM-250 catalyst There is only one endothermic peak corresponding to dehydration. It indicates that the ammonium salts deposited on HM-250 catalyst are hardly detected by thermal analyses. 

The most reliable method for making the enone is to alkylate the Mannich base with Mel and then treat the ammonium salt with base. Enolate ion formation leads to an ElcB reaction rather like the dehydration of aldols, but with a better leaving group. 

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