Purification, general acid chlorides

The phenylbenzamide is prepared from the acid chloride in the presence of Et3N (86% yield) and can be cleaved with 3% Na(Hg) (MeOH, 25°, 4 h, 81% yield). Most amides react only slowly with Na(Hg). Phenylbenzamides are generally crystalline compounds, an aid in their purification. ... 

Barton Esterification Reductive Decarboxylation. O-Acyl thiohydroxamates or Barton esters are useful precursors of carbon-centered radicals via thermolysis or photolysis. Several different methods are available for converting carboxylic acids into Barton esters (eq 1). These reactions generally proceed via the attack of a 2-mercaptopyridine-N-oxide salt on an activated carboxylic acid that has either been preformed (acid chloride, mixed anhydride) or generated in situ (with 1,3-dicyclohexylcarbodiimide or tri-n-butylphosphine + 2,2 -dithiodipyridine-l,r-dioxide). However, HOTT has the distinct advantages of (1) being easy to prepare and handle without the need for any special precautions, (2) facilitates efficient Barton esterification of carboxylic acids, and (3) simplifies subsequent work-up and purifications by avoiding the need to remove by-products like 1,3-dicyclohexylurea. 

A -( 1-Chloro- or bromoalkyl)amides are generally moisture-sensitive, unstable compounds, which are often directly used without further purification. Standard Lewis acids such as boron trifluoride-diethyl ether, aluminum(lll) chloride, zinc(II) chloride, tin(IV) chloride and titani-um(IV) chloride are used to generate the /V-acyliminium ion, although sometimes a catalyst is not necessary. 

General Considerations. The following chemicals were commercially available and used as received 3,3,3-Triphenylpropionic acid (Acros), 1.0 M LiAlH4 in tetrahydrofuran (THF) (Aldrich), pyridinium dichromate (Acros), 2,6 di-tert-butylpyridine (Acros), dichlorodimethylsilane (Acros), tetraethyl orthosilicate (Aldrich), 3-aminopropyltrimethoxy silane (Aldrich), hexamethyldisilazane (Aldrich), tetrakis (diethylamino) titanium (Aldrich), trimethyl silyl chloride (Aldrich), terephthaloyl chloride (Acros), anhydrous toluene (Acros), and n-butyllithium in hexanes (Aldrich). Anhydrous ether, anhydrous THF, anhydrous dichloromethane, and anhydrous hexanes were obtained from a packed bed solvent purification system utilizing columns of copper oxide catalyst and alumina (ether, hexanes) or dual alumina columns (tetrahydrofuran, dichloromethane) (9). Tetramethylcyclopentadiene (Aldrich) was distilled over sodium metal prior to use. p-Aminophenyltrimethoxysilane (Gelest) was purified by recrystallization from methanol. Anhydrous methanol (Acros) was... 

The procedure described below is quite general and uses finely, freshly machine--powdered KOH, which is added to a solution of the primary or secondary (acetylenic) alcohol and a 10-15% molar excess of tosyl chloride in Et20, kept around 0 C The excess of tosyl chloride is destroyed during the reaction of the excess of KOH. Side- and subsequent reactions ("saponification of the ester by KOH and 1,2-elimination of p-toluenesulfonic acid from thtfester) can be suppressed by keeping the temperature of the reaction mixture below 5 C. This procedure can be carried out within 2 h and generally gives excellent (often almost quantitative) yields of the tosylates. Purification of acetylenic tosylates by distillation, which is risky because of the limited thermal stability of the esters, is not necessary because the... 

Chemical treatment of natural waters. Both directly and indirectly, the general problem of purification and treatment of natural waters is related to the chemical and physical properties of the normal and acid salts of carbonic acid. The common impurities in natural waters consist of suspended solid organic and inorganic materials and of certain dissolved salts, particularly the acid carbonates, chlorides, and sulfates of sodium, calcium, and magnesium. The solid matter may be removed by filtration, the presence of limited quantities of sodium salts is not objectionable, and the calcium and magnesium salts are eliminated only through appropriate chemical treatment. The ions that are most... 

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