BASES AND SALTS

The hydrosilylation of carbonyl compounds by EtjSiH catalysed by the copper NHC complexes 65 and 66-67 constitutes a convenient method for the direct synthesis of silyl-protected alcohols (silyl ethers). The catalysts can be generated in situ from the corresponding imidazolium salts, base and CuCl or [Cu(MeCN) ]X", respectively. The catalytic reactions usually occur at room tanperature in THE with very good conversions and exhibit good functional group tolerance. Complex 66, which is more active than 65, allows the reactions to be run under lower silane loadings and is preferred for the hydrosilylation of hindered ketones. The wide scope of application of the copper catalyst [dialkyl-, arylalkyl-ketones, aldehydes (even enoUsable) and esters] is evident from some examples compiled in Table 2.3 [51-53],... 

Organic compounds, sulphur-, phosphorous- and nitrogen-compounds may be present as soluble, suspended or colloidal particles. This also holds for salts, bases and heavy metals. Pretreatment can change the physical state of pollutants in the wastewater. This gives a possibility for guiding the treatment process. 

Inorganic salts, bases and acids pH adjustment, chromatography column operations, cleaning, and buffer solutions for storage... 

The following reaction between a phosphonium salt, base, and an aldehyde gives a hydrocarbon Q Hi2 with the 200 MHz NMR spectrum shown. Give a structure for the product and comment on its stereochemistry. You are not expected to discuss the chemistry ... 

In recent years, many chiral catalysts for the enantioselective synthesis of optical active 1,5-dicarbonyl compounds have been developed, such as chiral crown ethers with potassium salt bases and chiral palladium complexes, including bimetallic systems. Nakajima and coworkers reported on enantioselective Michael reactions of S-keto esters to a,/3-unsaturated carbonyl compounds in the presence of a chiral biquinoline N,N dioxide-scandium complex, which catalyzed the additions in high yields and with enan-tioselectivities up to 84% ee . Kobayashi and coworkers found that the combination of Sc(OTf)3 with the chiral bipyridine ligand 149 (equation 41) was also effective as a chiral catalyst for asymmetric Michael additions of 1,3-dicarbonyl compounds 147 to a,/3-unsaturated ketones 148. The corresponding Michael adducts 150 were obtained in good to high yields with excellent enantiomeric excesses in most cases (Table 10). 

In some cases, aUc5me hydrothiolation can be achieved in the absence of transition metal catalysts. Examples include the use of indium halides, selenium halides and salts, bases and p-cyclodextrin [215-226]. In particular, Cesium bases yield exclusively the anti-Markovnikov product and fi equently give high regioselectivity for the Z-linear olefin, which is complementary to transition metal catalysis. While these approaches as yet lack the generality of the transition metal-catalyzed systems, the ability to achieve hydrothiolation without the need for a metal catalyst is attractive. Undoubtedly, this area of research will continue to yield promising results. 

A. Irreversible Colloids. — Some irreversible colloids are sensitive to electrolytes, while others remain unaffected. Some degree of r u-larity of behavior is manifested only by colloidal metals (free from contamination with other colloids), salts, and sulfides. Here the law obtains with a fair amount of certainty, that electrolytes cause precipitation. In general very small concentrations of salts, bases, and acids suffice to coagulate the colloid in question. The precipitate is not soluble in water. Nonelectrolytes, on the contrary, usually do not cause coagulation. The sensitiveness may be completely destroyed by the addition of often very small quantities of protective colloids. Even traces of these last-named substances may influence the reaction to a considerable degree. 

For ionized solvents which do not contain protons a base is a substance which reacts with the acid of that system to give a salt and the solvent. Thus the base KBrp4 reacts with the acid BrFiSbFfi to give the salt KSbF and Brp3 in bromine trifluoride. 

Ethylamine, monoethylamine, CH3CH2NH2-B.p. 19 C. Prepared by reduction of acetonitrile or by heating ethyl chloride with alcoholic ammonia under pressure. It is a strong base and will displace ammonia from ammonium salts. Forms a crystalline hydrochloride and also crystalline compounds with various metallic chlorides. 

This marked difference in colour between a base and its salts is also exemplified in the case of aminoaXolicnzcMie (p. 208). 

Aminoazobenzene is a very weak base, and consequently it will not form salts with weak organic acids, such as acetic acid, although it will do so with the strong mineral acids, such as hydrochloric acid. Aminoazobenzene is a yellowish-brown compound, whilst the hydrochloride is steel blue. The colour of the latter is presumably due to the addition of the proton to the phenyl-N-atom, the cation thus having benzenoid and quinonoid forms ... 

Aldehydes and ketones may frequently be identified by their semicarbazones, obtained by direct condensation with semicarbazide (or amino-urea), NH,NHCONH a compound which is a monacidic base and usually available as its monohydrochloride, NHjCONHNH, HCl. Semicarbazones are particularly useful for identification of con jounds (such as acetophenone) of which the oxime is too soluble to be readily isolated and the phenylhydrazone is unstable moreover, the high nitrogen content of semicarbazones enables very small quantities to be accurately analysed and so identified. The general conditions for the formation of semicarbazones are very similar to those for oximes and phenylhydrazones (pp. 93, 229) the free base must of course be liberated from its salts by the addition of sodium acetate. 

Aniline hydrochloride, being a salt formed from a very weak base and a strong acid, undergoes considerable hydrolysis in aqueous solution to aniline... 

Three years after the Breslow report on the large effects of water on the rate of the Diels-Alder reaction, he also demonstrated tliat the endo-exo selectivity of this reaction benefits markedly from employing aqueous media . Based on the influence of salting-in and saltirg-out agents, Breslow pinpoints hydrophobic effects as the most important contributor to the enhanced endo-exo... 

Michael condensations are catalyzed by alkaU alkoxides, tertiary amines, and quaternary bases and salts. Active methylene compounds and aUphatic nitro compounds add to form P-substituted propionates. These addition reactions are frequendy reversible at high temperatures. Exceptions are the tertiary nitro adducts which are converted to olefins at elevated temperatures (24). 

The reaction is generally carried out at atmospheric pressure and at 350—400°C. A variety of catalysts, eg, bases and metal salts and oxides on siUca or alumina—sihcates, have been patented (86—91). Conversions are in the 30—70% range and selectivities in the 60—90% range, depending on the catalyst and the ratio of formaldehyde to acetate. 

World installed capacity for formic acid is around 330,000 t/yr. Around 60% of the production is based on methyl formate. Of the remainder, about 60% comes from Hquid-phase oxidation and 40% from formate salt-based processes. The largest single producer is BASF, which operates a 100,000 t/yr plant at Ludwigshafen in Germany. The only significant U.S. producer of formic acid is Hoechst-Celanese, which operates a butane oxidation process. 

Xanthan gum dissolves in acids and bases, and under certain conditions, the viscosity remains stable for several months. Xanthan gum has exceUent StabiHty and compatibUity with high concentrations of many salts, eg, 15% solutions of sodium chloride and 25% solutions of calcium chloride (79). 

After sulfuric acid work-up (accompanied by the formation of sodium sulfate), the resorcinol is extracted and isolated in a 94% yield based on y -benzenedisulfonic acid [98-48-6]. In addition to the technical complexity that goes along with the manipulation of soHds at high temperature, this process produces large amounts of salts (sulfite and sulfate salts) which economically as well as environmentally are not always desired. 

Membranes and Osmosis. Membranes based on PEI can be used for the dehydration of organic solvents such as 2-propanol, methyl ethyl ketone, and toluene (451), and for concentrating seawater (452—454). On exposure to ultrasound waves, aqueous PEI salt solutions and brominated poly(2,6-dimethylphenylene oxide) form stable emulsions from which it is possible to cast membranes in which submicrometer capsules of the salt solution ate embedded (455). The rate of release of the salt solution can be altered by surface—active substances. In membranes, PEI can act as a proton source in the generation of a photocurrent (456). The formation of a PEI coating on ion-exchange membranes modifies the transport properties and results in permanent selectivity of the membrane (457). The electrochemical testing of salts (458) is another possible appHcation of PEI. 

Weak acid cation exchangers have essentially no abiUty to spHt neutral salts such as sodium chloride [7647-14-5]. On the other hand, an exchange is favorable when the electrolyte is a salt of a strong base and a weak acid. 

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