Hydroxides, alkali

Chlorine at normal temperature and atmospheric pressure is a yellow-greenish gas heavier than air (1 lit. of gas weighs 3.2204 g at 0 °C and 760 inm Hg). When cooled it condenses to form a liquid boiling at —34 °C (at 760 mm Hg) at —102 °C it solidifies into a yellow cristalline substance. The critical temperature of chlorine is 144 °C and the critical pressure 76.1 atm. Chlorine dissolves comparatively well in water, but its solubility is considerably reduced by the presence of sodium chloride. Chlorine dissolves better in organic solvents than in water, e. g. in dichlorethane, carbon tetrachloride etc. 

Two compounds of oxygen and chlorine are known chlorine monoxide and dioxide. When chlorine dioxide reacts with solutions of bases, chlorates are formed as well as salts of chlorous acid which are popular bleaching agents. 

When chlorine is brought into contact with solutions of alkali hydroxides hypochloratos or chlorates are formed in addition to chlorides, according to the reaction conditions. Chlorates may be thermally decomposed to form salts of perchloric acid. 

Chlorine in the technical sphere is very widely applied. Tho most important of these applications are  

In the chemical industry chlorine is used for the production of various chemical compounds, such as hydrochloric acid, hypochlorites, chlorates, bleaching powder, aluminium chloride, corrosive sublimate, cupric chloride, carbon tetrachloride, tin recovery from used cans, sulphuryl chloride, for extraction of bromine from Stassfurt waste liquors, etc. In the organic chemical industry it is used for the chlorination of aliphatic and cyclic organic compounds, for the preparation of medicaments, the manufacture of plastics, insecticides, fungicides and herbicides. Monochloracetic acid, ethylene chlorhydrine, chloral, chlor- 

---

BrCHi CHjBr. A colourless liquid with a sweet odour, m.p. 10°C, b.p. 132°C. Manufactured by passing ethene through bromine or bromine and water at about 20 C. Chemical properties similar to those of 1,2-dichloroethane when heated with alkali hydroxides, vinyl bromide is formed. Used extensively in petrols to combine with the lead formed by the decomposition of lead tetraethyl, as a fumigant for stored products and as a nematocide. 

Titanium IV) oxide, T1O2. See titanium dioxide. Dissolves in concentrated alkali hydroxides to give titanates. Mixed metal oxides, many of commercial importance, are formed by TiOj. CaTiOj is perovskite. BaTiOa, per-ovskite related structure, is piezoelectric and is used in transducers in ultrasonic apparatus and gramophone pickups and also as a polishing compound. Other mixed oxides have the il-menite structure (e.g. FeTiOj) and the spinel structure (e.g. MgjTiO ). 

Zinc(ll) hydroxide is a white gelatinous solid obtained when the stoichiometric quantity of alkali hydroxide is added to a solution of a zinc salt ... 

Alkali hydroxide gives a white precipitate solubie in excess. The white precipitate, Zn(OH)2, gives the oxide when dehydrated the white yellow reversible colour change observed on heating the oxide is a useful confirmatory test. 

Addition of an alkali hydroxide to a solution of a silver(I) salt gives a brown solid, silver(I) oxide, AgjO when wet, this behaves as silver hydroxide AgOH, for example... 

Mercury 11) compounds in solution give a black precipitate with hydrogen sulphide or a yellow precipitate with alkali hydroxide (pp. 437. 438). 

Sodium and potassium hydroxides. The use of these efficient reagents is generally confined to the drying of amines (soda lime, barium oxide and quicklime may also be employed) potassium hydroxide is somewhat superior to the sodium compound. Much of the water may be first removed by shaking with a concentrated solution of the alkali hydroxide. They react with many organic compounds (e.g., acids, phenols, esters and amides) in the presence of water, and are also soluble in certain organic liquids so that their use as desiccants is very limited... 

By hydrolysis of alkyl cyanides (or nitriles) with alkali hydroxide solutions, for example ... 

Cool the solution in ice while the alkali hydroxide is dissolving some ammonia gas is evolved. When the potassium hydroxide has dissolved, separate the amine, and dry it for 24 hours over sodium hydroxide pellets. Filter into a Claisen flask and distil. Collect the di-n-butylamine at 157-160°. The yield is 31 g. 

If acetaldehyde is warmed with a concentrated solution of an alkali hydroxide, it is converted into a resinous product resulting from repeated aldol condensations between aldol, crotonaldehyde and acetaldehyde. 

The formation of the above anions ("enolate type) depend on equilibria between the carbon compounds, the base, and the solvent. To ensure a substantial concentration of the anionic synthons in solution the pA" of both the conjugated acid of the base and of the solvent must be higher than the pAT -value of the carbon compound. Alkali hydroxides in water (p/T, 16), alkoxides in the corresponding alcohols (pAT, 20), sodium amide in liquid ammonia (pATj 35), dimsyl sodium in dimethyl sulfoxide (pAT, = 35), sodium hydride, lithium amides, or lithium alkyls in ether or hydrocarbon solvents (pAT, > 40) are common combinations used in synthesis. Sometimes the bases (e.g. methoxides, amides, lithium alkyls) react as nucleophiles, in other words they do not abstract a proton, but their anion undergoes addition and substitution reactions with the carbon compound. If such is the case, sterically hindered bases are employed. A few examples are given below (H.O. House, 1972 I. Kuwajima, 1976). 

Tantalum Oxides. Tantalum pentoxide [1314-61 -0] Ta20, (mp = 1880°C, density = 8.73 g/cm ) is a white powder existing in two thermodynamically stable modifications. The orthorombic P-phase changes at 1360°C into the tetragonal a-modiftcation. The existence of an S-modiftcation has also been reported (70). Tantalum pentoxide reacts slowly with hot hydrofluoric acid but is insoluble in water and in most solutions of acids and alkalies. For analytical purposes, it can be dissolved by fusion with alkali hydroxides, alkali carbonates, and potassium pyrosulfate. 

The presence of catalyst residues, such as alkali hydroxide or alkali acetate, a by-product of the hydrolysis reaction, is known to decrease the thermal stability of poly(vinyl alcohol). Transforming these compounds into mote inert compounds and removal through washing are both methods that have been pursued. The use of mineral acids such as sulfuric acid (258), phosphoric acid (259), and OfXv o-phosphotic acid (260) has been reported as means for achieving increased thermal stability of the resulting poly(vinyl alcohol). 

Laudanine, C20H25O4N, was isolated by Hesse. The crude alkaloid is purified by recrj stallisation from dilute alcohol for the removal of small quantities of cryptopine, or it may be dissolved in acetic acid and the solution poured into dilute caustic soda, when this impurity is precipitated and laudanine may be recovered from the filtrate by addition of ammonium chloride. It still contains its isomeride laudanidine, which may be separated by repeated crystallisation of the hydrochlorides, laudanidine accumulating in the aqueous mother liquors. The base crystallises from dilute alcohol, or from a mixture of alcohol and chloroform in rhombic prisms, m.p. 166°, [a]o 0°. It dissolves in solutions of alkali hydroxides, fornung metallic derivatives, which are precipitated by excess of alkali, but is nearly insoluble in solution of ammonia. The salts crystallise well ... 

CO reads al elevated temperatures to give formates with alkali hydroxides, and aeetates with raethoxides ... 

Sn02, cassiterite, is the main ore of tin and it crystallizes with a rutile-type structure (p. 961). It is insoluble in water and dilute acids or alkalis but dissolves readily in fused alkali hydroxides to form stannates M Sn(OH)6. Conversely, aqueous solutions of tin(IV) salts hydrolyse to give a white precipitate of hydrous tin(IV) oxide which is readily soluble in both acids and alkalis thereby demonstrating the amphoteric nature of tin(IV). Sn(OH)4 itself is not known, but a reproducible product of empirical formula Sn02.H20 can be obtained by drying the hydrous gel at 110°, and further dehydration... 

The saturated 2,2 -bis-oxazolones (10) are conveniently prepared [Eq. (7)] in two-steps via iV, iV -diacylbis-(a-amino acids), which cyclize in hot acetic anhydride. If R is aliphatic, alkali hydroxides... 

Heating of aryl halides or aryl sulfonates with alkali hydroxide,... 

The reaction can be performed with base catalysis as well as acid catalysis. The former is more common here the enolizable carbonyl compound 1 is depro-tonated at the a-carbon by base (e.g. alkali hydroxide) to give the enolate anion 5, which is stabilized by resonance ... 

Diketones 1 can be converted into the salt of an a-hydroxy carboxylic acid upon treatment with alkali hydroxide after acidic workup the free a-hydroxy carboxylic acid 2 is obtained. A well-known example is the rearrangement of benzil (R, R = phenyl) into benzilic acid (2-hydroxy-2,2-diphenyl acetic acid). The substituents should not bear hydrogens a to the carbonyl group, in order to avoid competitive reactions, e.g. the aldol reaction. 

Aldehydes 1 that have no a-hydrogen give the Cannizzaro reaction upon treatment with a strong base, e.g. an alkali hydroxide.In this disproportionation reaction one molecule is reduced to the corresponding alcohol 2, while a second one is oxidized to the carboxylic acid 3. With aldehydes that do have a-hydrogens, the aldol reaction takes place preferentially. 

When the arenediazonium compound 1 is treated with sodium acetate, instead of alkali hydroxide, the reaction proceeds via an intermediate nitroso compound, and is called the Hey reaction. 

The a -halosulfone, required for the Ramberg-Backlund reaction, can for example be prepared from a sulfide by reaction with thionyl chloride (or with N-chlorosuccinimide) to give an a-chlorosulfide, followed by oxidation to the sulfone—e.g. using m-chloroperbenzoic acid. As base for the Ramberg-Backlund reaction have been used alkoxides—e.g. potassium t-butoxide in an etheral solvent, as well as aqueous alkali hydroxide. In the latter case the use of a phase-transfer catalyst may be of advantage. ... 

For the classical Williamson synthesis an alcohol is initially reacted with sodium or potassium to give an alkoxide, e.g. 1. Alternatively an alkali hydroxide or amide may be used to deprotonate the alcohol. Phenols are more acidic, and can be converted to phenoxides by treatment with an alkali hydroxide or with potassium carbonate in acetone. ... 

The classical procedure for the Wolff-Kishner reduction—i.e. the decomposition of the hydrazone in an autoclave at 200 °C—has been replaced almost completely by the modified procedure after Huang-Minlon The isolation of the intermediate is not necessary with this variant instead the aldehyde or ketone is heated with excess hydrazine hydrate in diethyleneglycol as solvent and in the presence of alkali hydroxide for several hours under reflux. A further improvement of the reaction conditions is the use of potassium tcrt-butoxide as base and dimethyl sulfoxide (DMSO) as solvent the reaction can then proceed already at room temperature. ... 

This compound is a white, crystalline compound melting at 256°-257°C with decomposition. It is readily soluble in concentrated aqueous alkali hydroxide solutions and in concentrated aqueous mineral acids. 

Molten alkali hydroxides are particularly dangerous, not only because of scale fluxing, but also because they induce stress corrosion where stress is a serious factor. 

Fig. 73. Activity coefficients of alkali hydroxides in aqueous solution at 2S°C.

The alkali metals react vigorously with water (Figure 20.6) to evolve hydrogen and form a water solution of the alkali hydroxide. The reaction of sodium is typical ... 

---