REAGENTS FOR MICROCRYSTAL IDENTIFICATIONS 



dining effectiveness for precipitation. Crys- 

 tallizing effectiveness varies with the kind of 

 substances tested, and is greatest when a 

 resultant compound is neither too soluble 

 nor excessively insoluble. When insolu- 

 bility is very high, the precipitate is likely 

 to come down amorphous, and crystalliza- 

 tion may not be obtainable. However, the 

 very best tests combine ease of obtaining 

 crystals with a high sensitivity which usu- 

 ally means great insolubility of the product 

 formed. 



All these media have specific effects dis- 

 tinct from the general solubility effect. 

 Combinations of media are used to get the 

 best possible results in some cases. 



The reagents may be added to aqueous 

 solutions of the substances tested (the tra- 

 ditional way), usually without a cover glass; 

 or, particularly those with high concentra- 

 tion of acid, direct to a very little of the 

 solid substance, usually with a cover glass 

 added. 



In the list below, the major reagents of the 

 most widely applicable precipitating com- 

 pounds are given first, then a selection of 

 others, more or less in the order of declining 

 precipitating power, so far as this can be 

 reconciled with a certain listing of related 

 reagents together and related compounds 

 near each other. The list as a whole will be 

 found to bear but little resemblance to lists 

 of traditional ''alkaloidal reagents", al- 

 though the best of the traditional reagents 

 are included. 



Iodine-Iodide Reagents 



The precipitating compound, iodine-HI or 

 iodine-KI, or presumably the anion Is", has 

 the widest range of any. However, the con- 

 ditions for precipitation and suitable crys- 

 tals vary greatly depending on the type of 

 substance, and more types of reagents are 

 used than for any other precipitating com- 

 pound. Only those of greatest established 

 value are given here. Inorganic applications 

 certainly exist, at least with reagents made 



with H3PO4 , but have not been studied by 

 anyone, to the writer's knowledge. 



With Phosphoric Acid. (1) lodine-HI- 

 H,PO, reagciU. Iodine 0.08 g, HI (57%) 0.5 

 ml, syrupy H3PO4 (85-88%) 3.5 ml. May 

 be kept in a small rubber-bulb dropping 

 bottle. Remake when it has lost considerable 

 iodine strength. Very wide range of pre- 

 cipitation, but precipitates of many sub- 

 stances remain amorphous or in drops. Used 

 for crystals with various sympathomimetics, 

 aminoacetic acid, etc. (direct addition). 



(2) Iodine-KI reagent B-1. Mix 2 ml 

 iodine-KI solution (5 g iodine and 80 g KI 

 in water to make 100 ml) with 4 ml syrupy 

 H3PO4. Pour off from any KI that crystal- 

 lizes out. The mixed reagent keeps quite 

 well in an 8-ml rubber-bulb dropping bottle. 

 Used for barbiturates and similar compounds 

 (added to the slightly alkaline aqueous solu- 

 tion); also (added directly to the hydro- 

 chloride) for some of the simplest amines, 

 etc. 



(3) Iodine-KI reagent M-2. Mix 2 ml I-KI 

 solution (5:30 g in 100 ml) with 3 ml coned 

 HCl and 3 ml syrupy H3PO4 . Used espe- 

 cially for morphine (direct addition). 



With Acetic Acid. (4) Iodine-KI reagent 

 C-3. Mix 0.4 ml iodine-KI solution (10:10, 

 dissolved in about 15 ml water, then diluted 

 to 100 ml), 2.0 ml glacial acetic acid, 3.2 ml 

 water, 0.4 ml (1 -f 3) H2SO4 . Remake when 

 it loses strength. Used especially for ciuinine, 

 and for other cinchona alkaloids, which 

 form iodosulfate crystals; also for codeine, 

 etc. (direct addition). Wide range of useful 

 crystallization with complex compounds. 



(5) Iodine-KI reagent 0-1. Mix 4 ml 

 aqueous I-KI reagent No. 2 (1 : 1.75 g in 100 

 ml) with 2 ml glacial acetic acid. Originally 

 labeled "0-1" because of crystals with a 

 number of the opium alkaloids and their 

 synthetic modifications. 



Aqueous. (6) Concentrated aqueous iodine 

 reagents. Three of these have already been 

 mentioned when used as stock solutions. 

 They may also be used as reagents added to 



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