Chloride trapping

The diol function of 130 was protected as its acetonide 131 (88 %). Next, the enone function was installed by a-selenation of the enoxysilane, followed by peroxide oxidation and elimination (57 % over two steps). Finally, the unsaturated ketone 132 was homologated by 1,4-addition of trimethylsilylmethyl magnesium chloride, trapping with chlorotrimethylsilane, and reoxidation, to afford the target 117 (88 %). 

The gas released during the reaction should be vented through a calcium chloride trap to the back of an efficient hood. 

It is usual to carry out the reaction in water or ethanol, or in mixtures of the two, at temperatures ranging from 60° to the boiling point, for from 2 to 12 hours. Butanol has also been used as a solvent [82, 136] and, exceptionally xylene [137] and dimethylformamide [138], or even no solvent at all [136] The alkyl mercaptan which is evolved in this reaction can be absorbed in a solution of sodium hydroxide and hydrogen peroxide [135] or in a charcoalicupric chloride trap [139]. The guanidines are often conveniently isolated via their relatively insoluble bicarbonates [118, 139]. 

A minobenzophenone. In a dry 3-1. three-necked flask equipped with a stirrer, a reflux condenser connected to a hydrogen chloride trap, and a thermometer extending to the bottom of the flask are... 

Into a 500 ml spherical flask, equipped with a dropping funnel, a mechanical stirrer, a thermometer and a condenser, above which was disposed a calcium chloride trap, were introduced 16.95 g (0.141 mol) of ethyl cyanacetate and 40.69 g (0.33 mol) of n-propyl bromide. This mixture was heated to 45°C and then there was added thereto, slowly and while stirring, the previously prepared solution of sodium n-propylate, keeping the temperature of the reaction medium at 50°-55°C by gentle external cooling. 

With allyl chlorides, trapping of the product with an electrophile in situ (which can even be a reactive ketone such as cyclohexanone) prevents homocoupling reactions 32... 

B. 3,6-Diacety 1-9,10-dimethoxyphenanthrene. A 1-L, three-necked, round-bottomed flask, fitted with an addition funnel, mechanical stirrer, and hydrogen chloride trap, is charged with 23.7 g of 9,10-dimethoxyphenanthrene and 120 mL of CH2CI2 (Note 3). The solution is cooled in an ice-bath, and acetyl chloride (120 mL, (Note 4)) is added slowly. The cooling bath is removed, and over the course of 5 min, 44 g (0.33 mol) of aluminum chloride (Note 5) is added in portions to the stirred solution. The mixture is stirred for 15 min at ambient temperature and then carefully poured onto 1 L of crushed ice. The organic phase is separated, and the aqueous phase is extracted three times with 120-mL portions of CH,C1,. The combined organic phases are washed with 120 mL of water, then with 120 mL of saturated... 

The introduction of the trimethylsilyl chloride trapping technique" led to improved yields in the case of simple aliphatic esters. The initial silylated products are easily isolated and can be converted into the acyloins simply and in high yield. For simple aliphatic esters the yields are in the range 56-92%. Use of trimethylsilyl esters, rather than simple alkyl esters, leads to faster reactions, but lower yields.Substituted esters which have been successfully used in the newer procedure include ethyl 2-ethylhexanoate (83%), ethyl trimethylsilylacetate (90%)," ethyl 3-trimethylsilylpropionate (65%)," ethyl phenylacetate (48%)," ethyl 3-phenylpropionate (79%)" and 2-(2-methoxycarbonylethyl)-2-methyl-l,3-dioxolane derived from levulinic acid (65%)." In the case of ethyl adamantane-l-carboxylate the yield using the newer procedure is reported to be inferior to that using the earlier procedure. 

There is to date no reliable data on the amount of Cl sequestered by the hydrate cage because the physical separation of the water released by natural hydrate dissociation from pore water contamination can be very difficult. Suess et al. (2001) suggest that there may be residual chloride trapped within the hydrate pore space. Nevertheless, since this number is small and very poorly defined, most estimates of hydrate abundance in marine sediments assume that hydrate formation excludes all dissolved ions. 

Various attempts were made to determine the nature of the reactive o-xylylene species. In previous results [Ilia], a,a -dibromo-m-xylene reacted with metallic nickel to give a presumed ra-xylene bis(nickel bromide) species 6, which was effectively trapped with acetyl chloride to give the diketone product 7 in 62% yield (Scheme 7.3). Attempted acetyl chloride trapping of an o-xylene... 

Chloride microtraps were produced through the surface modification of silica particles by using known procedures. 3-Glydoxypropyltrimethoxysilane is hydrolyzed on silica particles starting from the hydroxyl groups resulting in the modification of their surfeces. This process leads to the formation of amine groups that act as chloride traps. Complete description of the fabrication procedure is described in the literature [1]. 

Figures 1.14 and 1.15 show the gas chromatograms of pyrolysis products trapped in 0.01 N H2SO4 solution, for acrylic acid containing latex A and methacrylic acid containing latex B, respectively. In the latex A case (Figures 1.14, 1.15), the 0.01 N H2SO4 solution-trapped products revealed a significant reduction in complexity of peaks and the acrylic acid and methacrylic acid peaks are better resolved from other pyrolysis products. This is a direct result of the low solubility of the nonpolar pyrolysis products in the polar solution. In contrast, the methanol and methylene chloride-trapped products exhibit gas chromatograms of about the same complexity as direct Py-GC pyrograms. This indicates that the selection of 0.01 N H2-SO4 solution as the trapping solvent can properly separate the acrylic acid or methacrylic acid from an abundance of other components...

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