Traces of water

C2H3N. Colourless liquid with strong ammoniacal smell b.p. 56 C. Miscible with water and strongly basic. Prepared commercially from 2-aminoelhanol. Pure dry aziridine is comparatively stable but it polymerizes explosively in the presence of traces of water. Carbon dioxide is sufficiently acidic to promote polymerization. 

Qualitative examples abound. Perfect crystals of sodium carbonate, sulfate, or phosphate may be kept for years without efflorescing, although if scratched, they begin to do so immediately. Too strongly heated or burned lime or plaster of Paris takes up the first traces of water only with difficulty. Reactions of this type tend to be autocat-alytic. The initial rate is slow, due to the absence of the necessary linear interface, but the rate accelerates as more and more product is formed. See Refs. 147-153 for other examples. Ruckenstein [154] has discussed a kinetic model based on nucleation theory. There is certainly evidence that patches of product may be present, as in the oxidation of Mo(lOO) surfaces [155], and that surface defects are important [156]. There may be catalysis thus reaction VII-27 is catalyzed by water vapor [157]. A topotactic reaction is one where the product or products retain the external crystalline shape of the reactant crystal [158]. More often, however, there is a complicated morphology with pitting, cracking, and pore formation, as with calcium carbonate [159]. 

N.B. A trace of water is required to make the forward reaction proceed at a realistic rate.)... 

Other examples of water as an apparent catalyst are (a) carbon monoxide will not bum in oxygen unless a trace of water is present. 

Chlorine reacts with most elements, both metals and non-metals except carbon, oxygen and nitrogen, forming chlorides. Sometimes the reaction is catalysed by a trace of water (such as in the case of copper and zinc). If the element attacked exhibits several oxidation states, chlorine, like fluorine, forms compounds of high oxidation state, for example iron forms iron(III) chloride and tin forms tin(IV) chloride. Phosphorus, however, forms first the trichloride, PCI3, and (if excess chlorine is present) the pentachloride PCI5. 

For this preparation, it is particularly necessary that the sodium acetate should be free from traces of water. The anhydrous material can be prepared by gently heating the hydrated salt (CHsCOONa,3HjO) in an esaporating-basin over a small Bunsen flame. The salt dissolves in its water of ciystallisation and resolidifies as this water is driven off further heating then causes the anhydrous material to melt. Stir the molten anhydrous material to avoid charring, and then allow it to cool in a desiccator. Powder the cold material rapidly in a mortar, and bottle without delay. 

Caution.—If the ethanol used to extract the methylamine hydrochloride is not absolute, i.e., if it contains traces of water, considerably less than the above suggested quantity will be required for the extraction, because the solubility of the hydrochloride will be markedly increased by the water present. The recrystallised material will now, however, contain traces of ammonium chloride. 

R NHa + C.HjNCO = RNH CO NHC,Hj Traces of water will contaminate the product with diphenylurea (p. 336) if the solution is boiled hence the need for anhydrous conditions. i-Naphthylisocyanate reacts more slowly with water, and the i-naphthyl-urea derivative can often be obtained using a cold aqueous solution of an aliphatic amine it is particularly necessary in such cases to purify the product by recrystallisation from, or extraction with, boiling petroleum, leaving behind any insoluble di i-naphthylurea. Note that the amine must also be free from alcohols (p. 335) and phenols (p. 337). 

The anhydrous compound is not appreciably hygroscopic, is readily soluble in acetone and amyl alcohol, and insoluble in benzene, toluene, xylene and chloroform it is also readily soluble in absolute methyl or ethyl alcohol, but a trace of water causes immediate hydrolysis with the formation of an opalescent precipitate. 

The reaction with sodium is by no means an infallible practical test for alcohols since, strictly speaking, it is applicable only to pure anhydrous liquids. Traces of water, present as impurities, would give an initial evolution of hydrogen, but reaction would stop after a time if an alcohol is absent furthermore, certain esters and ketones also evolve hydrogen when treated with sodium (compare Section XI,7,6). It may, however, be assumed that if no hydrogen is evolved in the test, the substance is not an alcohol. 

To obtain maleic acid, evaporate the maleic anhydride with one half of its weight of water on a water bath remove the last traces of water by leaving in a desiccator over concentrated sulphuric acid. The resulting maleic acid has m.p. 143° and is quite pure (1). It may be recrystaUised, if desired, from acetone- light petroleum (b.p. 60-80°) and then melts at 144° (1). 

RCH=N—ONa and R R C=N—ONa) which may be filtered off and washed with methanol to remove traces of sodium methoxide. It should be kept moist with methanol the sodium derivative, if allowed to dry, may become very explosive. Also, upon contact with a trace of water, it is liable to decompose with explosive violence. The sodium derivative may be dissolved by successively adding small quantities to cold water with continual stirring. 

To the best of our knowledge the data in Table 3.2 constitute the first example of enantio selectivity in a chiral Lewis-acid catalysed organic transformation in aqueous solution. Note that for the majority of enantioselective Lewis-acid catalysed reactions, all traces of water have to be removed from the... 

Note 1. Traces of water, or peroxides, formed during long periods of storage may inactivate the K0-tert.-Ci,Hq. 

The bottoms from the solvent recovery (or a2eotropic dehydration column) are fed to the foremns column where acetic acid, some acryflc acid, and final traces of water are removed overhead. The overhead mixture is sent to an acetic acid purification column where a technical grade of acetic acid suitable for ester manufacture is recovered as a by-product. The bottoms from the acetic acid recovery column are recycled to the reflux to the foremns column. The bottoms from the foremns column are fed to the product column where the glacial acryflc acid of commerce is taken overhead. Bottoms from the product column are stripped to recover acryflc acid values and the high boilers are burned. The principal losses of acryflc acid in this process are to the aqueous raffinate and to the aqueous layer from the dehydration column and to dimeri2ation of acryflc acid to 3-acryloxypropionic acid. If necessary, the product column bottoms stripper may include provision for a short-contact-time cracker to crack this dimer back to acryflc acid (60). 

The inactivity of pure anhydrous Lewis acid haUdes in Friedel-Crafts polymerisation of olefins was first demonstrated in 1936 (203) it was found that pure, dry aluminum chloride does not react with ethylene. Subsequentiy it was shown (204) that boron ttifluoride alone does not catalyse the polymerisation of isobutylene when kept absolutely dry in a vacuum system. However, polymers form upon admission of traces of water. The active catalyst is boron ttifluoride hydrate, BF H20, ie, a conjugate protic acid H" (BF20H) . 

By-product water formed in the methanation reactions is condensed by either refrigeration or compression and cooling. The remaining product gas, principally methane, is compressed to desired pipeline pressures of 3.4—6.9 MPa (500—1000 psi). Einal traces of water are absorbed on siHca gel or molecular sieves, or removed by a drying agent such as sulfuric acid, H2SO4. Other desiccants maybe used, such as activated alumina, diethylene glycol, or concentrated solutions of calcium chloride (see Desiccants). 

Friedel-Crafts (Lewis) acids have been shown to be much more effective in the initiation of cationic polymerization when in the presence of a cocatalyst such as water, alkyl haUdes, and protic acids. Virtually all feedstocks used in the synthesis of hydrocarbon resins contain at least traces of water, which serves as a cocatalyst. The accepted mechanism for the activation of boron trifluoride in the presence of water is shown in equation 1 (10). Other Lewis acids are activated by similar mechanisms. In a more general sense, water may be replaced by any appropriate electron-donating species (eg, ether, alcohol, alkyl haUde) to generate a cationic intermediate and a Lewis acid complex counterion. 

Properties. The physical properties of magnesium hydroxide are Hsted in Table 8. The crystalline form of magnesium hydroxide is uniaxial hexagonal platelets (Fig. 4). Magnesium hydroxide begins to decompose thermally above 350°C, and the last traces of water are driven off at higher temperatures to yield magnesia. 

Because phosgene reacts with water, great care must be taken to prevent contamination with traces of water since this could lead to the development of pressure by hydrogen chloride and carbon dioxide. Wet phosgene is very corrosive therefore phosgene should never be stored with any quantity of water (4). 

The reaction of NaOH with bisphenol A generates water. This water must be thoroughly removed from the system to allow the reaction to be driven to completion, and more importandy, to preclude any residual water in the system from hydrolyzing part of the DCDPS monomer (2). Before the introduction of DCDPS for the polymerization step, all but traces of water must be removed. Failure to do so results in regeneration of NaOH, which rapidly reacts with DCDPS to form the monosodium salt of 4-chloro-4 -hydroxydiphenylsulfone [18995-09-0] (3) (6). 

Physical Properties. Sodium metabisulfite (sodium pyrosulfite, sodium bisulfite (a misnomer)), Na2S20, is a white granular or powdered salt (specific gravity 1.48) and is storable when kept dry and protected from air. In the presence of traces of water it develops an odor of sulfur dioxide and in moist air it decomposes with loss of part of its SO2 content and by oxidation to sodium sulfate. Dry sodium metabisulfite is more stable to oxidation than dry sodium sulfite. At low temperatures, sodium metabisulfite forms hydrates with 6 and 7 moles of water. The solubiHty of sodium metabisulfite in water is 39.5 wt % at 20°C, 41.6 wt % at 40°C, and 44.6 wt % at 60°C (340). Sodium metabisulfite is fairly soluble in glycerol and slightly soluble in alcohol. 

Stannic Chloride. Stannic chloride is available commercially as anhydrous stannic chloride, SnCl (tin(IV) chloride) stannic chloride pentahydrate, SnCl 5H20 and in proprietary solutions for special appHcations. Anhydrous stannic chloride, a colorless Aiming Hquid, fumes only in moist air, with the subsequent hydrolysis producing finely divided hydrated tin oxide or basic chloride. It is soluble in water, carbon tetrachloride, benzene, toluene, kerosene, gasoline, methanol, and many other organic solvents. With water, it forms a number of hydrates, of which the most important is the pentahydrate. Although stannic chloride is an almost perfect electrical insulator, traces of water make it a weak conductor. 

The oxide monobutyltin oxide [51590-67-1J, is a sesquioxide, C H SnO from which it is difficult to remove the last traces of water. It is an infusible, insoluble, amorphous white powder that forms when butyltin trichloride is hydrolyzed with base. The partially dehydrated material, butylstaimoic acid [2273-43-0] is slightly acidic and forms alkaH metal salts. These salts, ie, alkaH metal alkylstaimonates, form when excess alkaH is used to hydrolyze the organotin trichloride ... 

The primary Cr—O bonded species is cbromium (VT) oxide, CrO, which is better known as chromic acid [1115-74-5], the commercial and common name. This compound also has the aliases chromic trioxide and chromic acid anhydride and shows some similarity to SO. The crystals consist of infinite chains of vertex-shared CrO tetrahedra and are obtained as an orange-red precipitate from the addition of sulfuric acid to the potassium or sodium dichromate(VI). Completely dry CrO is very dark red to red purple, but the compound is deflquescent and even traces of water give the normal mby red color. Cbromium (VT) oxide is a very powerful oxidi2er and contact with oxidi2able organic compounds may cause fires or explosions. 

The heating with freshly dehydrated lime not only removes traces of water, but gives a product which is entirely free from halogen. 

Drying is carried out in the flask in which the final reaction is to be run in order to avoid a transfer. The success of this preparation depends upon the exclusion of moisture. The silver salt retains traces of water tenaciously. 

---