Anhydrous preparation

Calcium sulfate (anhydrous). (Prepared by heating the dihydrate or the hemihydrate in an oven at 235° for 2-3h it can be regenerated.) Available commercially as Drierite. It forms the hemihydrate, 2CaS04.H20, so that its capacity is fairly low (6.6% of its weight of water), and hence is best used on partially dried substances. It is very efficient (being comparable with phosphorus pentoxide and concentrated sulfuric acid). Suitable for most organic compounds. Solvents boiling below 100° can be dried by direct distillation from calcium sulfate. 

V-Acryloxysuccinimide anhydrous copolymerization with V-isopropylacrylamide, 246 preparation, 246 V-Acryloxysuccinimide-V-isopropylacrylamide copolymer anhydrous preparation, 248,250/... 

Acetic acid, anhydrous, preparation of, 295 2-AcetoxyisopropyIazobenzene, 330 Acetylene... 

The cause of the promotional effect is not clear. Probably the chromium attaches somewhat differently to a dehydrated surface than to one which is fully hydroxylated. A higher concentration of dichromate, instead of chromate, is one possible cause since the remaining hydroxyls are more widely spread. The promotional effect could also be due to a strained attachment which is frozen to the surface by the low binding temperature. Heating these anhydrously prepared catalysts at 900°C destroys the promotional effect, leaving only an ordinary aqueous type catalyst. Probably the increased mobility at 900°C relaxes the strain or rearranges the Cr(VI) back to its usual mode of attachement. 

When anhydrous preparative methods are employed, such as direct reaction between the metal and Hthd, the tetramer Ba4(thd)8, which has been shown to exist in two slighly different crystalline forms, is obtained (see Fig. 32).177 178180 Under similar reaction conditions, strontium forms the trimeric compound Sr3(tmhd)<1(Htmhd) (Fig. 33).177 Both compounds contain chelating and bridging /3-diketonate ligands. The bonding modes of these ligands vary to achieve metal coordination numbers of 6-8. The... 

Figure 3. Adsorption isotherm of argon on anhydrous preparation of sodium bromide at 77.5° K...

The M-heterocyclic quaternary salts of nonaromatic enamines, such as the tialkyl-3,4,5,6-tetrahydropyridines, A-l-pyrrolines, and 5.6-dihydro-2//-thiazincs. are very sensitive to water, and molecular sieves need to be used in conjunction with azeotroping to keep the reaction mixture anhydrous. Preparing and handling these intermediates and spiro compounds2 from them requires great care. 

Nitric Acid, Anhydrous. Prepared by distillation of coned nitric acid with coned sulfuric acid by treating so -dium or potassium nitrate with 100% H2S04 and removing HN03by distillation by fractional crystallization of coned HN03, Review of preparation and properties of pure HNOy Stern et a/, Chet i. Rev, 60, 185-207 (I960), See also Niiric Acid. 

Factors affecting drug absorption physicochemical factors 169 Anhydrous preparation... 

If a licensed product has to be adapted, the pharmacist should suggest a standard pharmacy preparation with a comparable base and chemical form of the active substance. For example the type of emulsion has to be the same or an anhydrous formulation such as a hydrophilic or hydrophobic ointment should be replaced with a similar anhydrous preparation. 

Scheme 2. Mitsui decoupled anhydrous preparation with polyol additives...

Scheme 3. Amoco anhydrous preparation with in-situ generation of the reducing agent... 

In one case, in particular, Roush observed the elimination of a silyl ether even with an anhydrous preparation of TASF. However, inclusion of several equivalents of water attenuated the basicity of the fluoride and produced the desired product in good yield without competitive elimination. Anhydrous TASF does foster similar side reactions with some highly sensitive substrates, such as those found during the synthesis of bafilomycin Al, (—)-osmundalactone, and (—)-muricatacin. While HF pyridine andHF EtsN are alternative reagents for base sensitive substrates, reactivity problems are often encountered, leading to very slow or incomplete reactions, or even no reaction. However, TASF in a solution of DMF/water (2-3 equiv of water relative to the amount of TASF) appears to be even milder than the anhydrous reagent, as shown in the synthesis of bafilomycin Al. ... 

Several micro-organisms can survive and propagate on unpreserved cosmetic products. Preservatives are routinely added to all preparations that can support microbial growth. The choice of a preservative for a given product is difficult. Anhydrous preparations and products containing high levels of ethanol or t-propanol may not require the addition of preservatives. 

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