Intermediate fractions

Carry out a second run with the recovered chloroform-alcohol mixture (A) add 100 g. of dry chloroform and sufficient super-dry ethyl alcohol (200-250 ml.) to give a total volume of 750 ml. Add 52 g. of sodium as before. Remove the excess of chloroform and attohol as before on a water bath through a fractionating column, add the intermediate fraction (B) from the first run, and fractionate again. The yield of product b.p. 144-146°, is 45 g. 

In most cases boiling points of small, intermediate fractions are given, instead of the more usual boiling ranges. 

The cmde tall oil fatty acids obtained from the rosin column usually contain about 5% rosin because the boiling points of the heavier fatty acids and the lighter resin acids overlap. By adding the intermediate fraction to the fatty acid, rosin does not have to be redistilled. 

Coarse solids are discharged by siphons extending to the bottom of the hindered-settling zone. Siphon control is obtained by a novel hydrostatically actuated valve which makes or breaks the siphon to flow only when the teeter zone is in correct condition. Discharge by an intermediate fraction from the upper column is by means of additional siphons. Hydraulic-water consumption is considerably lower than required for multipocket sizers. 

The difference between the distillation and pot temperatures is closely related to the success of this preparation. If the specified weights of reactants and temperatures are employed a 3 temperature difference should be reached before the yellow intermediate fraction, probably containing methanesulfenyl chloride, chloromethanesulfenyl chloride, and acetic acid, has attained a volume of 10 ml. Toward the end of the distillation the pot temperature may begin to rise owing to the presence in the residue of methanesulfonyl chloride (b.p. 63°/20 mm.,... 

The crude anhydride is carefully fractionated through a 13-mm. x 1.2-m. Nester still at a pressure of 25 mm. (Note 4) and a reflux ratio of at least 10 1. After a fore-run of maleic anhydride, b.p. 50-100°/25 mm., and a small intermediate fraction, there is obtained 75-90 g. (22-26%) of 3-methylenecyclobutane-l,2-dicar-boxylic anhydride b.p. 155-159°/25 mm. 1.4935-1.4952 (Note 5). This material is of sufficient purity for most uses, but it contains approximately 2-5% of propargylsuccinic anhydride. Redistillation through the Nester still gives 65-80 g. (19-23%) of 3-methylenecyclobutane-l,2-dicarboxylic anhydride b.p. 155°/25 mm. 1.4946-1.4955. 

Collection of the product fraction should begin after a few milliliters of an intermediate fraction has been collected at 155°/25 mm. This material has a low index of refraction. 

Endo-a-(l-44)-poiygalacturonase digestion gave three fragments eluted in the void volume (PG-lc), intermediate fraction (PG-2c) and the iowest-molecular-weight fraction (PG-3c) from GR-2IIc [6]. Methylation analysis using base-catalyzed -elimination... 

These opposing tendencies may defeat the purpose of the fractional precipitation process. The fractional precipitation of crystalline polymers such as nitrocellulose, cellulose acetate, high-melting polyamides, and polyvinylidene chloride consequently is notoriously inefficient, unless conditions are so chosen as to avoid the separation of the polymer in semicrystalline form. Intermediate fractions removed in the course of fractional precipitation may even exceed in molecular weight those removed earlier. Separation by fractional extraction should be more appropriate for crystalline polymers inasmuch as both equilibrium solubility and rate of solution favor dissolution of the components of lowest molecular weight remaining in the sample. 

As the rate of take-off is reduced near the end of a fraction, a slight lowering of the bath temperature may be necessary to avoid flooding of the column. Also as the boiling point rises during the collection of the intermediate fraction, the power input to the jacket must be increased in order to hold its temperature just below the boiling point. 

The reaction mixture at the end was treated carefully with water, and washed. The reaction mixture was analysed at this point by gel permeation chromatography (GPC). The high polymer could be isolated by precipitation in isopropylalcohol. The intermediate fraction PII was partly precipitated with the PHI or remained in solution according to the conditions of the reaction. Further fractions of PII could be isolated by precipitation in ethanol or methanol. PI was soluble in ethanol. 

For reaction rate expressions oT the ftth-order form it can be shown that there is always one and only one point that minimizes the total volume when n > 0. This situation is obtained when the intermediate fraction conversion /x is selected so that the slope of the curve representing the reaction rate expression at this conversion level is equal to the slope of the diagonal of rectangle KLMN, as shown in Figure 8.13, adopted from Levenspiel. Once this conversion level is known, equations 8.3.34 and 8.3.35 may be used to determine the required reactor sizes. 

A small amount of the alcohol comes over at 51-52°/200 mm and then, after the heating bath is replaced, 4-6 cc. of an intermediate fraction distils. This is followed by a fraction which boils at 83-86°/200 mm. and which is collected as pure ketene acetal. A total of 78-87 g. is obtained (67-75 per cent of the theoretical amount). The major portion is collected while the temperature of the bath is 120-140°, and the remainder is obtained by raising the bath temperature to 170-180°. 

The most widely used complexing agents are alcohols (butanol, n-propyl alcohol and n-pentyl alcohol1). Schoch33 now recommends the use of Pen-tasol, a commercial mixture of pentyl alcohols, for the first precipitation, and 1-butanol for recrystallizations. For com (maize) starch, this avoids contamination of the amylopectin with an intermediate fraction which is sufficiently linear to be precipitated with Pentasol and yet has a degree of branching which prevents complex formation with butanol. 

Polymerizations often afford polymodal product molecular weight distributions,18 with typically a low molecular weight fraction of several hundred daltons (fraction I), an intermediate fraction of about 4,000 (fraction II) and then a high molecular weight fraction of 10s or 106 (fraction III), though the relative proportions of the fractions depend... 

The preparation described here of 3-cyclopentene-1-carboxylic acid from dimethyl malonate and cis-1,4-dichloro-2-butene is an optimized version of a method reported earlier3 for obtaining this often used and versatile building block.6 The procedure is simple and efficient and requires only standard laboratory equipment. 3-Cyclopentene-1-carboxylic acid has previously been prepared through reaction of diethyl malonate with cis-1,4-dichloro(or dibromo)-2-butene in the presence of ethanolic sodium ethoxide, followed by hydrolysis of the isolated diethyl 3-cyclopentene-1,1-dicarboxylate intermediate, fractional recrystallization of the resultant diacid to remove the unwanted vinylcyclopropyl isomer, and finally decarboxylation.2>7 Alternatively, this compound can be obtained from the vinylcyclopropyl isomer (prepared from diethyl malonate and trans-1,4-dichloro-2-butene)8 or from cyclopentadiene9 or cyclopentene.10 In comparison with the present procedure, however, all these methods suffer from poor selectivity, low yields, length, or need of special equipment or reagents, if not a combination of these drawbacks. 

Figure 1. Compositional distribution of a predominantly syndiotactic copolymer bearing COCHiSOsN(CHs)t units (DPn = 650, DSm = O 366) from precipitation fractionation data. System 1 (6) CHCls—Et2C) system II (O) DMF—Hs0 + O, 5% NH4Cl cross fractionation ( ) intermediate fractions obtained from system II are further fractionated according to System I.

Fractionation is the basic refining process for separating crude petroleum into intermediate fractions of specified boihng point ranges. The various subprocesses include prefractionation and atmospheric fractionation, vacuum fractionation, and three-stage crude distillation. 

Purities of the end products in the procedures are generally > 95%. The boiling points given refer to small intermediate fractions. 

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