Hydroxides, dehydrations

Much more stable complexes are formed from silanolate active centres and oxides, hydroxides or partly dehydrated hydroxides of amphoteric metals [106], A polymer whose centres have been complexed in this way is completely resistant to depolymerization even at 523 This situation is illustrated in Fig. 10. 

Also the thermo-oxidative stability of the deactivated polymer is excellent. At the present time, hydroxides and partially dehydrated hydroxides of amphoteric metals, especially of aluminium, are applied as additives suppressing the flammability of polymers. 

In low-polarity media, specific interaction with protic species (water) dramatically affects the reactivity (nucleophilicity or basicity) of anions with high charge density (OH. F. oxanions. carbanions, etc.). Basicity of OH in the Hofinann elimination reaction of (hexyl)4 N 0H /7H20 (Eq. 9), carried out in a chlorobenzene-water two-phase system, increases 50.000 times by reducing the hydration number n of the anion from 11 to 3. The enhancement is extrapolated to be more than nine powers of 10 for the hypothetical anhydrous hydroxide. This indicates that the largely dehydrated hydroxide, extracted in a low-polarity solvent (chlorobenzene) from concentrated alkaline soluiions. is an extremely powerful base. Results account for the dramatic effect produced by an increase of base on the rate of reactions promoted by alkali hydroxides under LL-PTC conditions, such as carbanion formation and alkylation, alkene isomerization, H/D exchanges in carbon acids, and acid-base equilibria ... 

It is readily dehydrated on warming, to give the black oxide CuO. It dissolves in excess of concentrated alkali to form blue hydroxo-cuprate(II) ions, of variable composition it is therefore slightly amphoteric. If aqueous ammonia is used to precipitate the hydroxide, the latter dissolves in excess ammonia to give the deep blue ammino complexes, for example [Cu(NH3)4(H20)2] ... 

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. 

Both forms sublime very readily, even at room temperature a small sample on exposure to the air will completely volatilise in a short time, particularly on a warm day or if the sample is exposed to a gentle current of air. Hence the above method for rapid drying. A sample confined in an atmospheric desiccator over calcium chloride rapidly disappears as the vapour is adsorbed by the calcium chloride. A sample of the hexahydrate similarly confined over sodium hydroxide undergoes steady dehydration with initial liquefaction, for the m.p. of the hydrated-anhydrous mixture is below room temperature as the dehydration proceeds to completion, complete resolidification occurs. 

If crystallised barium hydroxide (Ba(OH) 8H,0) is employed, this becomes dehydrated after one run the anhydrous compound is just as satisfactory and may be used repeatedly. 

Styrene may be conveniently prepared in the laboratory by heating p-phenylethyl alcohol (Section IV,204) with sohd sodium or potassium hydroxide when an almost quantitative dehydration occurs ... 

The metallic salts of trifluoromethanesulfonic acid can be prepared by reaction of the acid with the corresponding hydroxide or carbonate or by reaction of sulfonyl fluoride with the corresponding hydroxide. The salts are hydroscopic but can be dehydrated at 100°C under vacuum. The sodium salt has a melting point of 248°C and decomposes at 425°C. The lithium salt of trifluoromethanesulfonic acid [33454-82-9] CF SO Li, commonly called lithium triflate, is used as a battery electrolyte in primary lithium batteries because solutions of it exhibit high electrical conductivity, and because of the compound s low toxicity and excellent chemical stabiUty. It melts at 423°C and decomposes at 430°C. It is quite soluble in polar organic solvents and water. Table 2 shows the electrical conductivities of lithium triflate in comparison with other lithium electrolytes which are much more toxic (24). 

Medroxyprogesterone acetate (74) is stmcturaHy related to and has been prepared from hydroxyprogesterone (39) (Fig. 10). Formation of the bis-ketal accomplishes the protection of the ketones and the required migration of the double bond. Epoxidation with peracetic acid produces a mixture of epoxides (75), with a predominating. Treatment of the a-epoxide with methyl magnesium bromide results in diaxial opening of the epoxide. Deprotection of the ketones provides (76), which is dehydrated to (77) by treatment with dilute sodium hydroxide in pyridine. Upon treatment with gaseous hydrochloric... 

In the three-step process acetone first undergoes a Uquid-phase alkah-cataly2ed condensation to form diacetone alcohol. Many alkaU metal oxides, metal hydroxides (eg, sodium, barium, potassium, magnesium, and lanthanium), and anion-exchange resins are described in the Uterature as suitable catalysts. The selectivity to diacetone alcohol is typicaUy 90—95 wt % (64). In the second step diacetone alcohol is dehydrated to mesityl oxide over an acid catalyst such as phosphoric or sulfuric acid. The reaction takes place at 95—130°C and selectivity to mesityl oxide is 80—85 wt % (64). A one-step conversion of acetone to mesityl oxide is also possible. 

Figure 2 illustrates the three-step MIBK process employed by Hibernia Scholven (83). This process is designed to permit the intermediate recovery of refined diacetone alcohol and mesityl oxide. In the first step acetone and dilute sodium hydroxide are fed continuously to a reactor at low temperature and with a reactor residence time of approximately one hour. The product is then stabilized with phosphoric acid and stripped of unreacted acetone to yield a cmde diacetone alcohol stream. More phosphoric acid is then added, and the diacetone alcohol dehydrated to mesityl oxide in a distillation column. Mesityl oxide is recovered overhead in this column and fed to a further distillation column where residual acetone is removed and recycled to yield a tails stream containing 98—99% mesityl oxide. The mesityl oxide is then hydrogenated to MIBK in a reactive distillation conducted at atmospheric pressure and 110°C. Simultaneous hydrogenation and rectification are achieved in a column fitted with a palladium catalyst bed, and yields of mesityl oxide to MIBK exceeding 96% are obtained. 

Lead Hydroxide. Lead hydroxide [19781-14-3] Pb(OH)2, mol wt 241.23, starts to dehydrate at about 130°C, and decomposes to lead... 

Lithium ion is commonly ingested at dosages of 0.5 g/d of lithium carbonate for treatment of bipolar disorders. However, ingestion of higher concentrations (5 g/d of LiCl) can be fatal. As of this writing, lithium ion has not been related to industrial disease. However, lithium hydroxide, either dHectly or formed by hydrolysis of other salts, can cause caustic bums, and skin contact with lithium haHdes can result in skin dehydration. Organolithium compounds are often pyrophoric and requHe special handling (53). 

The cmde phthaUc anhydride is subjected to a thermal pretreatment or heat soak at atmospheric pressure to complete dehydration of traces of phthahc acid and to convert color bodies to higher boiling compounds that can be removed by distillation. The addition of chemicals during the heat soak promotes condensation reactions and shortens the time required for them. Use of potassium hydroxide and sodium nitrate, carbonate, bicarbonate, sulfate, or borate has been patented (30). Purification is by continuous vacuum distillation, as shown by two columns in Figure 1. The most troublesome impurity is phthahde (l(3)-isobenzofuranone), which is stmcturaHy similar to phthahc anhydride. Reactor and recovery conditions must be carefully chosen to minimize phthahde contamination (31). Phthahde [87-41-2] is also reduced by adding potassium hydroxide during the heat soak (30). 

Iron Oxide Yellows. From a chemical point of view, synthetic iron oxide yellows, also known as iron gelbs, are based on the iron(III) oxide—hydroxide, a-FeO(OH), known as goethite. Color varies from light yellows to dark buffs and is primarily determined by particle size, which is usually between 0.1 and 0.8 p.m. Because of their resistance to alkahes, these are used by the building industry to color cement. Thermally, iron oxide yellows are stable up to 177°C above this temperature they dehydrate to iron(III) oxide ... 

Eig. 1. The key steps for the Phillips PPS process are (/) production of aqueous sodium sulfide from aqueous sodium hydrogen sulfide (or hydrogen sulfide) and aqueous sodium hydroxide 2) dehydration of the aqueous sodium sulfide and NMP feedstocks 5) polymerization of the dehydrated sulfur source with -dichlorobenzene to yield a slurry of PPS and by-product sodium chloride in the solvent (4) polymer recovery (5) polymer washing for the removal of by-product salt and residual solvent (6) polymer drying (7) optional curing, depending on the appHcation and (< ) packaging. 

Tliese can be cyclized by heating in the presence of sodium hydroxide to give a dehydration product. Tlius monoalkaiiolaniines fomi 2-alkylaziridines. 

Aluminum hydroxide and aluminum chloride do not ionize appreciably in solution but behave in some respects as covalent compounds. The aluminum ion has a coordination number of six and in solution binds six molecules of water existing as [Al(H20)g]. On addition of a base, substitution of the hydroxyl ion for the water molecule proceeds until the normal hydroxide results and precipitation is observed. Dehydration is essentially complete at pH 7. 

Further deprotonation, dehydration, and polymerization of monomers and dimers may yield ringlike stmctures of hydroxy—aluminum complexes (10). Coalescence of ring compounds into layers by further growth results in the formation of crystalline aluminum hydroxide at pH 6, the point of minimum aqueous solubiUty. 

After epoxidation, propylene oxide, excess propylene, and propane are distilled overhead. Propane is purged from the process propylene is recycled to the epoxidation reactor. The bottoms Hquid is treated with a base, such as sodium hydroxide, to neutralize the acids. Acids in this stream cause dehydration of the 1-phenylethanol to styrene. The styrene readily polymerizes under these conditions (177—179). Neutralization, along with water washing, allows phase separation such that the salts and molybdenum catalyst remain in the aqueous phase (179). Dissolved organics in the aqueous phase ate further recovered by treatment with sulfuric acid and phase separation. The organic phase is then distilled to recover 1-phenylethanol overhead. The heavy bottoms are burned for fuel (180,181). 

Oxides and Hydroxides. ThaHous oxide is most readily obtained by dehydration of TlOH ia high vacuum at 50°C. It is black, crystalline, and hygroscopic. It reacts with water to form the hydroxide and dissolves ia ethanol to yield the ethoxide (9). 

The basic hydrolysis of tri alkyl tin haUdes and other salts forms bis(oxide)s since, except for trimethyl tin, hydroxides are unstable towards dehydration at room temperature. With tin aryl, aralkyl, and cycloalkyltin compounds, the hydroxides can be isolated. Although quite stable, they exist in mobile equiUbrium with the bisoxide and water and are easily dehydrated. Trimethyl tin hydroxide is exceptionally stable towards dehydration. 

Bis(trineophyltin) oxide [60268-17-4] is prepared from the chloride in the normal manner. The chloride can either be prepared directiy from the reaction of three moles of neophylmagnesium chloride and stannic chloride or by the butyl transfer reaction between butyltrineophyltin and stannic chloride. The hydroxide derivative initially formed on hydrolysis of the chloride is readily dehydrated to the bis(oxide) at ca 100°C. 

Anatase and mtile are produced commercially, whereas brookite has been produced by heating amorphous titanium dioxide, which is prepared from an alkyl titanate or sodium titanate [12034-34-3] with sodium or potassium hydroxide in. an autoclave at 200—600°C for several days. Only mtile has been synthesized from melts in the form of large single crystals. More recentiy (57), a new polymorph of titanium dioxide, Ti02(B), has been demonstrated, which is formed by hydrolysis of K Ti O to form 20, followed by subsequent calcination/dehydration at 500°C. The relatively open stmcture... 

The ferrous hydroxide then combines with oxygen and water to produce ferric hydroxide, Fe(OH)2, which becomes common iron mst when dehydrated to Fe202. 

Dehydration of 2inc hydroxide can then lead to formation of the thermodynamically more stable 2inc oxide. 

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