Acetal control

Determination of the catalytically active species derived from 1 in solution. Spectrophotoraetric titration of the backbone ligand 5 with copper(II) acetate in methanol revealed formation of a dinuclear copper(ll) complex species Cu2L.3h(OAc) above a 1 2 molar ratio. A mononuclear copper(ll) species CuL 2h (6) dominates at a 1 1 molar ratio of 5 and copper(ll) acetate. Control experiments for the assignment of putative structures based on the obtained spectroscopic data included a UVA is spectroscopic titration of 5 with anhydrous sodium acetate in the presence of copper(ll) chloride and revealed that acetate is necessary for the formation of a copper (11) complex in methanol. The composition of 1 in methanol is the same as determined by elemental analysis for the sohd state. 

Silyl-directed Beckmann fragmentation. A trimethylsilyl group in the p- or p -position of cyclic ketoxime acetates controls the regio- and stereochemistry of the double bond formed on Beckmann fragmentation catalyzed by trimethylsilyl triflate. 

Emmett M, Sirmon MD, Kirkpatrick WG, Nolan CR, Schmitt GW, Cleveland MB. Calcium acetate control of serum phosphorus in hemodialysis patients. Am J Kidney Dis 1991 17(5) 544-50. 

Suspension Polymerization of Vinyl Acetate (Control of Molecular Weight by... 

Suspension Polymerization of Vinyl Acetate (Control of Molecular Weight by Variation in Initiator Level) (Based on Bartl [4] and Bravar et al. [117])... 

The classical problem in carbohydrate chemistry of the stereocontrolled synthesis of p-mannopyranosides was largely solved by the introduction of the 4,6-0-benzylidene acetal controlled method in the mid-1990s. The main drawback to this method,... 

Abe, M. and Nojima, M., The Paterno-Biichi photocydoaddition reactions of silyl ketene acetals controlling factors on the regio- and stereoselectivity in the oxetane formation,/. Synth. Org. Chem. Jpn., 59, 855, 2001. 

One remaining possibility that is less costly from an energy point of view but needs to be carefully controlled is to incorporate additives called flow improvers. These materials favor the dispersion of the paraffin crystals and in doing so prevent them from forming the large networks which cause the filter plugging. The conventional flow improvers essentially change the CFPP and pour point, but not the cloud point. They are usually copolymers, produced, for example, from ethylene and vinyl acetate monomers ... 

The excess of unchanged acetic anhydride is then hydrolysed by the addition of water, and the total free acetic acid estimated by titration with standard NaOH solution. Simultaneously a control experiment is performed identical with the above except that the alcohol is omitted. The difference in the volumes of NaOH solution required in the two experiments is equivalent to the difference in the amount of acetic add formed, i.e., to the acetic acid used in the actual acetylation. If the molecular weight of the alcohol is known, the number of hydroxyl groups can then be calculated. 

The absolute concentration of a reagent e.g., the exact amount of acetic anhydride in the above pyridine. solution) need not be determined, since if the same amount of the reagent is used in the actual and in the control experiments, the difference gives at once the actual amount used. 

C.HsNH, + CHjCO-O-COCHa = C.R NHCOCHs -h CHjCOOH then hydrolysed with water and the total free acetic acid estimated by titration with standard NaOH solution, the result being compared with that obtained in a control or blank experiment. 

Similar activation takes place in the carbonylation of dimethyl ether to methyl acetate in superacidic solution. Whereas acetic acid and acetates are made nearly exclusively using Wilkinson s rhodium catalyst, a sensitive system necessitating carefully controlled conditions and use of large amounts of the expensive rhodium triphenylphosphine complex, ready superacidic carbonylation of dimethyl ether has significant advantages. 

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