Other Methods of Preparation

The attack of the proton is generally directly at the M-H bond, i.e., M is not protonated and then later transfers to the hydride. An initial hydrogen bonding interaction may facilitate the protonation (see Section 7.3 for kinetic studies), which usually gives the H2 complex as the product even when the dihydride may be the thermodynamically favored product [Eq. (3.11)].  

Normally the protonation is carried out at low temperatures to give a [M-H2] complex, but on warming there is sometimes rearrangement to a dihydride or equilibrium mixture. Occasionally the product is unstable toward loss of H2 and coordination of anion or solvent (S) if the electronics and thermodynamics of the system do not favor Hj binding [Eq. (3.12)]. 

The stability of Hj complexes prepared by protonation thus varies greatly Some are stable only below room temperature and cannot be isolated as solids and 

Needless to say, complexes formed by protonation, especially where HA is a strong acid, are readily deprotonated, even by bases as weak as diethyl ether, and are highly sensitive to solvent media and trace water. These properties relate in large measure to the high acidity of certain Hj complexes, which can have pK, as low as -6, e.g., when generated from triflic acid (see Chapter 9). 

Decomposition of OsH( / -H2BH2)(CO)(P Pr3)2 in methanol produced OsH2(H2)(CO)(P P3)2, which despite its wide use as a hydrogen transfer catalyst was not determined to have until nearly 10 years later,yet another example that illustrates how difficult it can be to prove the presence of Hj hgands Another vmusual synthesis involves hydrogenation of an ethylene complex either in solution or even in the solid state at 60°C [Eq. (3.14)]  

The chemistry of nitrofuroxans has been presented in detail in monograph [566] and review [567] therefore, here we consider works published after. 

3-Substituted l,5-diphenyl-4-nitropyrazoles are obtained from corresponding 3-pyrazolines, which slowly oxidize on standing in air [571], 

The 3- and 4-nitrosopyrazoles are easily oxidized to the corresponding nitro derivatives [22, 572, 573], 1-Aryl substituted 4-dimethylaminopyrazoles are converted into the 5-nitro derivatives by the action of nitrous acid [574, 575], 

2-(jV-Methylamino)-5-nitro-4-phenylthiazole has been prepared by interaction of 2-(/V-mcthyl-A -nitroamino)-4-phci]ylthia/olc with 50% sulfuric acid [578], The result indicates that migration of the A-nitro group occurs on the intramolecular path however, in concentrated sulfuric acid, formation of nitronium ion and ring nitration also takes place [578], 4-Nitro-5-azidoimidazole has been obtained from corresponding 5-diazo compound, and hydrazone steroids passed anticancer and antibacterial activity [579], 

Azido derivatives nitro-bis-l,2,4-triazoles a perspective hight energetic compounds have been prepared by functionalization or defunctionalization of (relative) 

Benzalacetone has been obtained in small yield by drv distillation of a mixture of calcium acetate and calcium cinnamate (1) by heating the sodium derivative of cinnamaldehyde with methyl iodide (2) by heating cinnamaldehyde and methyl alcohol with zinc chloride (2) by heating acetone and benzaldehyde with acetic anhydride or zinc chloride (3). It is also formed when styrene and acetyl chloride are condensed by means of stannic chloride and the product is treated with diethylaniline (4) and when the vapors of cinnamic acid and acetic acid are passed together over ferric oxide at 470-490° (5). The only practical method, however, consists in condensing benzaldehyde and acetone by means of dilute aqueous alkali (6). 

Copper 4-bromobenzenethiolate can be polymerized at 200°C in quinoline solution. Electron spin resonance spectroscopy shows the existence of organic free radicals throughout the polymerization. In addition, Cu + are observed. These phenomena suggest a radical mechanism of polymerization. It was early suspected that the reaction mechanism should not be a 

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A complete set of trihalides for arsenic, antimony and bismuth can be prepared by the direct combination of the elements although other methods of preparation can sometimes be used. The vigour of the direct combination reaction for a given metal decreases from fluorine to iodine (except in the case of bismuth which does not react readily with fluorine) and for a given halogen, from arsenic to bismuth. 

Bromoacetic acid can be prepared by the bromination of acetic acid in the presence of acetic anhydride and a trace of pyridine (55), by the HeU-VoUiard-Zelinsky bromination cataly2ed by phosphoms, and by direct bromination of acetic acid at high temperatures or with hydrogen chloride as catalyst. Other methods of preparation include treatment of chloroacetic acid with hydrobromic acid at elevated temperatures (56), oxidation of ethylene bromide with Aiming nitric acid, hydrolysis of dibromovinyl ether, and air oxidation of bromoacetylene in ethanol. 

Other methods of preparation of anhydrous ZrF include the decomposition of 7250-81-6] at 297°C (5). NH F sublimes and leaves... 

Other Asymmetric Membrane Preparation Techniques. A number of other methods of preparing membranes have been reported i the literature and are used on a small scale. Table 1 provides a brief summary of these techniques. 

Other methods of preparation have been described in detail (8,75,76). 

Various processes involve acetic acid or hydrocarbons as solvents for either acetylation or washing. Normal operation involves the recovery or recycle of acetic acid, any solvent, and the mother Hquor. Other methods of preparing aspirin, which are not of commercial significance, involve acetyl chloride and saHcyHc acid, saHcyHc acid and acetic anhydride with sulfuric acid as the catalyst, reaction of saHcyHc acid and ketene, and the reaction of sodium saHcylate with acetyl chloride or acetic anhydride. 

Stannic Oxide. Stannic oxide tin(IV) oxide, white crystals, mol wt 150.69, mp > 1600° C, sp gr 6.9, is insoluble in water, methanol, or acids but slowly dissolves in hot, concentrated alkaH solutions. In nature, it occurs as the mineral cassiterite. It is prepared industrially by blowing hot air over molten tin, by atomizing tin with high pressure steam and burning the finely divided metal, or by calcination of the hydrated oxide. Other methods of preparation include treating stannic chloride at high temperature with steam, treatment of granular tin at room temperature with nitric acid, or neutralization of stannic chloride with a base. 

Other methods of preparing tertiary bismuthines have been used only to a limited extent. These methods iaclude the electrolysis of organometaUic compounds at a sacrificial bismuth anode (54), the reaction between a sodium—bismuth or potassium—bismuth alloy and an alkyl or aryl haUde (55), the thermal elimination of sulfur dioxide from tris(arenesulfiaato)bismuthines (56), and the iateraction of ketene and a ttis(dialkylainino)bismuthine (57). 

There are other methods of preparation that iavolve estabhshing an active phase on a support phase, such as ion exchange, chemical reactions, vapor deposition, and diffusion coating (26). For example, of the two primary types of propylene polymerization catalysts containing titanium supported on a magnesium haUde, one is manufactured usiag wet-chemical methods (27) and the other is manufactured by ball milling the components (28). 

A chlorohydrin has been defined (1) as a compound containing both chloio and hydroxyl radicals, and chlorohydrins have been described as compounds having the chloro and the hydroxyl groups on adjacent carbon atoms (2). Common usage of the term appHes to aUphatic compounds and does not include aromatic compounds. Chlorohydrins are most easily prepared by the reaction of an alkene with chlorine and water, though other methods of preparation ate possible. The principal use of chlorohydrins has been as intermediates in the production of various oxitane compounds through dehydrochlorination. 

Other methods of preparation, eg, the reaction of CIF or BrF and CrO, yield the oxyfluoride contaminated with reactants and side reaction products. 

Other Methods of Preparation. In addition to the direct hydration process, the sulfuric acid process, and fermentation routes to manufacture ethanol, several other processes have been suggested. These include the hydration of ethylene by dilute acids, the hydrolysis of ethyl esters other than sulfates, the hydrogenation of acetaldehyde, and the use of synthesis gas. None of these methods has been successfilUy implemented on a commercial scale, but the route from synthesis gas has received a great deal of attention since the 1974 oil embargo. 

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