Picric acid in ethanol

The most versatile derivative from which the free base can be readily recovered is the picrate. This is very satisfactory for primary and secondary aliphatic amines and aromatic amines and is particularly so for heterocyclic bases. The amine, dissolv in water or alcohol, is treated with excess of a saturated solution of picric acid in water or alcohol, respectively, until separation of the picrate is complete. If separation does not occur, the solution is stirred vigorously and warmed for a few minutes, or diluted with a solvent in which the picrate is insoluble. Thus, a solution of the amine and picric acid in ethanol can be treated with petroleum ether to precipitate the picrate. Alternatively, the amine can be dissolved in alcohol and aqueous picric acid added. The picrate is filtered off, washed with water or ethanol and recrystallised from boiling water, ethanol, methanol, aqueous ethanol, methanol or chloroform. The solubility of picric acid in water and ethanol is 1.4 and 6.23 % respectively at 20°. 

Co[C6H(OH)(N02)3] 2 brown pdr (Refs 1, 3 4) or dk red crysts (from ale) (Refs 2 5) mp expl with moderate violence at 320-25°. Can be obtained on heating to ca 150° any of its hydrates, such as with 2-, 6- or 9.5-H20 (Refs 1 3). Tetra - and penta-hydrates are also reported (Ref 1). Bernardi Piacentini (Refs 2 5), reported prepn of anhydrous salt by treating picric acid in ethanol with Co hydroxide... 

Indolizidine has been made in 68% yield by the action of silver ions on JV-chloroazacyclononane in dioxane.231 Pyrrolizidine and quinolizi-dine have been prepared similarly but in much poorer yields. Also, 1-methyl-5-hydroxyazacyclononane gave a trans-iustd quaternary salt (172) when heated with either perchloric, hydriodic, or picric acid in ethanol.232 However, it is more usual to apply this reaction in the reverse direction for synthesis of medium ring compounds. 

The following are typical experimental details for the preparation of naphthalene picrate. Dissolve 0.1 g of naphthalene in the minimum of hot ethanol and add to 1 ml of a saturated solution of picric acid in ethanol. Warm the mixture and then cool to allow the product to crystallise. 

The following alternative procedure may sometimes be employed. Dissolve 0.5 g of the amine in 5 ml of rectified spirit and add 5 ml of a cold saturated solution of picric acid in ethanol. Warm on a water bath for 5 minutes and allow to cool. Collect the precipitated picrate and recrystallise it as above. 

Conductometric and spectrophotometric behavior of several electrolytes in binary mixtures of sulfolane with water, methanol, ethanol, and tert-butanol was studied. In water-sulfolane, ionic Walden products are discussed in terms of solvent structural effects and ion-solvent interactions. In these mixtures alkali chlorides and hydrochloric acid show ionic association despite the high value of dielectric constants. Association of LiCl, very high in sulfolane, decreases when methanol is added although the dielectric constant decreases. Picric acid in ethanol-sulfolane and tert-butanol-sulfolane behaves similarly. These findings were interpreted by assuming that ionic association is mainly affected by solute-solvent interactions rather than by electrostatics. Hydrochloric and picric acids in sulfolane form complex species HCl and Pi(HPi). ... 

Table III. The pK Values of Picric Acid in Ethanol— TMS and tert-Butanol— TMS Mixtures at 30°C...

Figure 9. Test of Equation 17 (n = 4) for ionization of picric acid in ethanol-TMS and text-butyl alchol-TMS mixtures (O), EtOH-TMS ( ),...

From the alkyl halide with thiourea in 95% ethanol, followed by additton of picric acid in ethanol For directions and examples see Lmstead, pp 82 3, Shriner, p 245, Vogel, pp 291 2, Wild, p 43, E L Brown and N Campbell, 7 Chem Soc, 1699 (1937), W J Levy and N Campbell, 7 Chem 5oc, 1442 (1939) From the alkyl halide with thiourea in ethylene glycol, followed by addition of picric acid in ethanol See Cheronis, p 550, H M Crosby and J B Entnkin, 7 Chem Ed, 41, 360 (1964)... 

From the aromatic ether with picric acid in ethanol... 

N-5 and N-6 participation may also lead to bicyclic heterocycles containing nitrogen. For example, 4,5-dichloro-N-methylcycloheptyl and octyl amines react with N-5 and N-6 participation to give products with inversion at the carbon undergoing displacement, e.g., Eq. (41). In a similar type of reaction, heating of the amino alcohols (70), (71), or (72) with HI, HCIO4, or picric acid in ethanol led to ring closure, e.g., Eq. (42). However, under similar conditions, (73) led only to dehydration. 

Preparation of picrates 2-Alkylbenzimidazole (50 —200mg) is dissolved in a minimum amount of hot ethanol, and the solution is added to a saturated solution of picric acid in ethanol. 

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