Crystallization from

Crystallizes from water in large colourless prisms containing 2H2O. It is poisonous, causing paralysis of the nervous system m.p. 101 C (hydrate), 189°C (anhydrous), sublimes 157°C. It occurs as the free acid in beet leaves, and as potassium hydrogen oxalate in wood sorrel and rhubarb. Commercially, oxalic acid is made from sodium methanoate. This is obtained from anhydrous NaOH with CO at 150-200°C and 7-10 atm. At lower pressure sodium oxalate formed from the sodium salt the acid is readily liberated by sulphuric acid. Oxalic acid is also obtained as a by-product in the manufacture of citric acid and by the oxidation of carbohydrates with nitric acid in presence of V2O5. 

The mixture of xylidines has been used as a first component of azo-dyes. The chief constituent of the mixture is m-xylidine (4-amino-1,3-xylene). It can be separated by crystallization from glacial ethanoic acid. It is also used for the preparation of azo-dyes. 

Fig. VII-4. Interactions across a dividing surface for a rare-gas crystal. (From Ref. 43.)...

Fig. VII-7. Motion of an edge dislocation in a crystal undeigoing slip deformation (a) the undeformed crystal (b, c) successive stages in the motion of the dislocation from right to left (d) the undeformed crystal. (From Ref. 113 with permission.)...

Fig. VIII-8. Surface structures (a) (1 x 1) structure on the (100) surface of a FCC crystal (from Ref. 76) (b) C(2 x 1) surface structure on the (100) surface of a FCC ciystal (from Ref. 76). In both cases the unit cell is indicated with heavy lines, and the atoms in the second layer with pluses. In (b) the shaded circles mark shifted atoms. (See also Ref. 77.)...

Because it is necessary to exclude some substances, including some crystals, from the Nemst heat theorem, Lewis and Gibson (1920) introduced the concept of a perfect crystal and proposed the following modification as a definitive statement of the third law of themiodynamics (exact wording due to Lewis and Randall (1923)) ... 

Leadbetter A J and Norris E K 1979 Distribution functions in hree liquid crystals from x-ray diffraction measurements Moiec. Phys. 38 669-86... 

A) Filtration of crystals from the cold mother-liquor. 

For solids which melt above 100° and are stable at this temperature, drying may be carried out in a steam oven. The crystals from the Buchner funnel should then be placed on a clock glass or in an open dish. The substance may sometimes be dried in the Buchner funnel itself by utilising the device illustrated in Fig. 77, <33, 1. An ordinary Pyrex funnel is inverted over the Buchner funnel and the neck of the funnel heated by means of a broad flame (alternatively, the funnel may be heated by a closely-fltting electric heating mantle) if gentle suction is applied to the Alter flask, hot (or warm) air will pass over the crystalline solid. 

You know how just a couple of paragraphs ago where the chemist first filtered the crude crystals from the chilled reaction mixture, then washed them with water or acetic acid Well, all that liquid filtrate has a lot of valuable, unreacted piperonal or benzaldehyde in it. To rescue the stuff the chemist dilutes the mixture with 500ml dHaO and extracts it with DCM. The DCM is washed with 100ml 5% NaOH solution then vacuum distilled to give a dark oil which is unreacted aldehyde. Hey That s a lot of good material that can be put through the process again. 

High vacuum distillation gave a crystalline product, containing small amounts of impurities, inter alia some 2-butynoic acid. Crystallization from a 3 1 mixture of pentane and diethyl ether at low temperature gave the pure acid, m.p. 77°C, in 38-45 yields. 

Very pure samples can be obtained by crystallization from pentane (see Ref. 11). 

In a similar way (CH3ChC)2S02 (m.p. 98-100°C, after one crystallization from diethyl ether-pentane) was prepared in 78% yield from (CH3CcC)2S (Chapter III, Exp. 37). 

The action of ammonia on N-(aryl-i,3-oxathiol-2-ylidine) tertiary im-inium salts (254) yields linear intermediates (255) that cyclize to 2-amino-4-phenyl thiazoles (256) on crystallization from acetic acid (Scheme 129) (730). 

Iodide ion (I ) Alkyl chlorides and bromides are converted to alkyl iodides by treatment with sodium iodide in acetone Nal is soluble in acetone but NaCI and NaBr are insoluble and crystallize from the reaction mixture making the reac tion irreversible... 

In spite of their easy interconversion in solution a and p forms of carbohydrates are capable of independent existence and many have been isolated m pure form as crys talline solids When crystallized from ethanol d glucose yields a d glucopyranose mp 146°C [a]o +112 2° Crystallization from a water-ethanol mixture produces p d glucopyranose mp 148-155°C [aj +18 7° In the solid state the two forms do not mterconvert and are stable indefinitely Their structures have been unambiguously con firmed by X ray crystallography... 

Ethyl bis-(2,4-dinitrophenyl) acetate (indicator) the stock solution is prepared by saturating a solution containing equal volumes of alcohol and acetone with the indicator pH range colorless 7.4-9.1 deep blue. This compound is available commercially. The preparation of this compound is described by Fehnel and Amstutz, Ind. Eng. Chem., Anal. Ed. 16 53 (1944), and by von Richter, Ber. 21 2470 (1888), who recommended it for the titration of orange- and red-colored solutions or dark oils in which the endpoint of phenol-phthalein is not easily visible. The indicator is an orange solid which after crystallization from benzene gives pale yellow crystals melting at 150-153.5°C, uncorrected. 

Single crystals such as those shown in Fig. 4.11 are not observed in crystallization from the bulk. Crystallization from dilute solutions is required to produce single crystals with this kind of macroscopic perfection. Polymers are not intrinsically different from low molecular weight compounds in this regard. 

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