Vapor-phase ammonium chloride

The vapor-phase conversion of aniline to DPA over a soHd catalyst has been extensively studied (18,22). In general, the catalyst used is pure aluminum oxide or titanium oxide, prepared under special conditions (18). Promoters, such as copper chromite, nickel chloride, phosphoric acid, and ammonium fluoride, have also been recommended. Reaction temperatures are usually from 400 to 500°C. Coke formed on the catalyst is removed occasionally by burning. In this way, conversions of about 35% and yields of 95% have been reported. Carba2ole is frequently a by-product. 

A.mmonium C/j/oride. Work on the distribution of ammonium chloride [12125-02-9] between the vapor andhquid phases (8) suggests that the Ray diagram is sometimes an oversimplification. In most steam systems, there is much more ammonia than any other impurity. In particular, there is more ammonia than hydrogen chloride. The volatiUty of ammonium chloride is therefore expressed by the following chemical equation ... 

Vinyl chloride reacts with ammonium chloride [12125-02-9] and oxygen in the vapor phase at 325°C over a cupric chloride [7447-39-4] CuCl, catalyst to make 1,1,2-trichloroethane and ammonia (68). 

Methyl chloride reacts with ammonia alcohoHc solution or ia the vapor phase by the Hofmann reaction to form a mixture of the hydrochlorides of methylamine, dimethylamine, trimethyl amine, and tetramethyl ammonium chloride. With tertiary amines, methyl chloride forms quaternary derivatives. 

Gas-phase reactions can also be used to produce products of low volatility that condense to give an aerosol. The reaction of gaseous NH3 with HC1 to form particles of solid ammonium chloride and the reaction of gaseous S03 with water vapor to form H2S04 are typical examples. Such methods tend to give submicron particles. 

Figure 1. Log-log plot of the density difference di — da between the liquid and vapor phase of ammonium chloride [34] and bismuth chloride [60] versus the temperature distance T— Tc from the critical temperature Tc. For comparison, data are also shown for xenon and ammonia. The slope of the straight line for NH4C1 is f = 0.5. The slopes of the other lines are / = 0.326. Redrawn with permission from M. Buback, Thesis, Karlsruhe 1969.

There were other, less theoretical but no less persuasive objections. Some substances, such as ammonium chloride, dissociate in the vapor phase. That is, a single particle of vapor turns into two or more particles. Two or more particles occupy two or more times the volume that one particle does. That wreaks havoc with measurements of gas volumes and provides empirical evidence that fails to obey Gay-Lussac s law, making apparent nonsense of Avogadro s hypothesis. It was not until the phenomenon of dissociation was understood, and interpreted in terms of reaction kinetics, that this objection could be countered. Similar objections were raised against Dalton s laws of combining proportions, which work only for compounds of fixed composition. Metallic alloys and salt solutions, to take two of the most obvious exceptions, do seem to share some of the characteristics of chemical compounds, but they do not fit Daltons laws. The simplest way to avoid that objection was to say that only those substances that did fit Dalton s laws were true chemical compounds, but that is a circular argument that did not convince critics. 

Acetylcholineesterase and choline oxidase Co-immobilizing AChE and ChO on to a Pt disc microelectrode (200 tM diameter) with glutaraldehyde vapor. Sensor was used in flow-injection and LC system at a potential of 0.6 V versus Ag/AgCl/ KC1 (saturated) with mobile phase containing 0.1 M-phosphate buffer (pH 8) (for FIA) and 0.05 M phosphate buffer at pH 7.5 containing 0.03 mM SDS and 3mM tetramethyl ammonium chloride (for LC). The LC separations were carried out on an ODS-5 column (25 cm x 0.5 mm i.d.). The microsensor exhibited a linear response for acetylcholine and choline for 0.05-103 pmol. [87]... 

Acetylene is condensed to vinylacetylene and divinylacetylene by cuprous chloride and ammonium chloride. Similar additions of other compounds containing an active hydrogen atom occur in the presence of various catalysts. Mercury salts ate most effective in the vapor-phase reaction of acetylene with hydrogen chloride to give vinyl chloride (100%). Basic catalysts such as potassium hydroxide, potassium ethoxide, or zinc oxide are used for the vinylation of alcohols, glycols, amines, and acids. Most of these reactions involve the use of acetylene under pressure, and few have been described as simple laboratory procedures. Chloroacetic acid, however, reacts with acetylene at atmospheric pressure in the presence of mercuric oxide to yield vinyl chloro-acetate (49%). ... 

Conversion of Phenols to Amines. Aniline and some diphenylamine are formed when phenol and NHs solution are heated under pressure in the presence of FeCh, Al(OH)s, or Fe(OH)j. When NH and phenol or ortho-or para-cresols are reacted in the vapor phase over an AljO catalyst, yields of up to 88 per cent of the corresponding amines are obtained. However, these amines are customarily obtained by reducing the parent nitro compound, except in cases where it is difficult to obtain the required nitro isomer. For example, it is considered that the amination of symr xylenol is the best method of preparing sym-xylidine (l-amino-3,5-di-methylbenzene). When sym-xylenol is heated under pressure to 320 C with ammonium chloride, about equal amounts of sj/m-xylidine and sym-dixylylamine (5-imino-bis-l,3-dimethylbenzene) are formed. The ortho-and para-nitrophenols and nitrocresols can be aminat more readily. 2-Nitro-p-cresol [OH(l), N02(2), CHj(4)] and o-nitrophenol have been aminated in aqueous ammonia containing ammonium salts of weak acids to inhibit decomposition. Phosphoric, boric, carbonic, and formic acids were used. In one case it is claimed that 55-65 per cent yields of 2-nitro-p-toluidine (MNPT of commerce) were obtained when 2-nitro-p-cresol, 28 per cent aqueous NHj, and monoammonium phosphate, 1 11.5 0.2 molar ratio, were heated under pressure for 10 hr at 140-150°C and then 5 hr at about 160 C. Earlier workers, employing somewhat similar conditions, claimed excellent yields of MNPT when 1 mole of ammonium formate was used per mole of 2-nitro-p-cresol. ... 

N4H4 is made by simple metathetic reaction in liquid, solid, or gaseous media which may involve distillation or precipitation. For example, equimolar amounts of ammonium chloride and sodium azide may be distilled with an equal quantity of water. At 160°C pot temperature, the product volatilizes with water vapors and solidifies in the condenser tube which should, therefore, be at least 1 inch wide [305]. Equally clean and safe is a gas-phase reaction which requires, however, the preparation of hydrazoic acid gas. The reaction takes place in a long, 1-inch-wide glass tube which has two inlet tubes with orifices 20 inches apart, and a vent. The HN3 gas, carried with nitrogen, and excess ammonia stream in and precipitate the product as fine needles [39]. N4H4 is also precipitated when ammonia gas is bubbled into an ethereal hydrazoic acid solution [86]. The product stays in solution when HN3 vapors, carried with nitrogen, are bubbled into aqueous ammonia [306]. 

Dichloroethane is produced by the vapor- (28) or Hquid-phase chlorination of ethylene. Most Hquid-phase processes use small amounts of ferric chloride as the catalyst. Other catalysts claimed in the patent Hterature include aluminum chloride, antimony pentachloride, and cupric chloride and an ammonium, alkaU, or alkaline-earth tetrachloroferrate (29). The chlorination is carried out at 40—50°C with 5% air or other free-radical inhibitors (30) added to prevent substitution chlorination of the product. Selectivities under these conditions are nearly stoichiometric to the desired product. The exothermic heat of reaction vapori2es the 1,2-dichloroethane product, which is purified by distillation. 

Post-synthesis modification involves isomorphous substitution of framework atoms with the desired redox metals either in aqueous media with soluble metal salts or in the gas phase with volatile chlorides. Incorporation of Ti into the framework of faujasite, zeolite-) and ZSM-5 has been accomplished by treating the zeolite with ammonium titanyl oxalate, TiCU or Ti(0/-Pr)4. Substitution of V for framework atoms has been reported with VOCI3 vapor. A more generalized method involving the reoccupation of the silanol nests created by the deboronation of bor-osilicates (ZSM-5 and zeolite- ) shows considerable promise for the incorporation of redox metals into the framework [79]. 

After aqueous impregnation, copper(II) chloride is present as a highly dispersed phase on the surface of zeolites. After a thermal treatment in nitrogen and subsequently in ammonia, the copper appears to be present as isolated ions in the zeolite. Therefore, impregnation is a suitable method to prepare non-acidic copper-zeolites. As copper vaporization is limited with a catalyst not having a cation excess, a zeolite pre-exchanged with ammonium ions and consecutively impregnated with copper seems especially suitable. 

---