Hydroxide method

The pyridine procedure may be apphed to the preparation of other esters they are isolated by ether extraction. The yields are generally better than by the sodium hydroxide method. 

Saponification of esters. Aqueous sodium hydroxide method. To hydrolyse an ester of an alcohol, reflux 5-6 g. with 50 ml. of 20 per cent, sodium hydroxide solution for 1-2 hours or until the ester layer disappears. Distil the alkahne mixture and collect about 6 ml. of distillate. This will contain any volatile alcohol formed in the saponification. If the alcohol does not separate, i.e., is water-soluble, saturate the distillate with sohd potassium carbonate an upper layer of alcohol is then usually formed. (The alcohol may be subsequently identified as the 3 5-dinitrobenzoate see Section 111,27,2.) Cool the residual alkahne mixture, and acidify it with dilute sulphuric acid. If no crystalline acid is precipitated, the acid may frequently be isolated by ether extraction, or it may be distilled from the acidified solution and isolated from (or investigated in) the distfllate. (The acid may be subsequently identified, e.g., as the S benzyl wo-thiuronium salt see Section 111,85,2.)... 

The determination of the saponification equivalent of an ester by the alcohohc potassium hydroxide method is described in Section 111,106 an alternative procedure using diethylene glycol is given below. This constant should be determined if possible in the prehminary examination, since a knowledge of its value together with the boihng point provides a basis for a fairly good approximation of the size of the ester molecule. 

Hydroxydeethoxylation of the 2>H- -benzazepine 3 in refluxing methanolic potassium hydroxide (Method A) is accompanied by selective hydrolysis and loss of the 3-carboxylate group.20 Hydrolysis in concentrated hydrochloric acid, however, is rapid and yields only the bcnz-azepinone 4 (Method B). 

Kurfuerst, M., Ghisla, S., and Hastings, J. W. (1986). Bacterial luciferase intermediates the neutral flavin semiquinone, its reaction with superoxide, and the flavin 4a-hydroxide. Method. Enzymol. 133 140-149. 

Bis[2-benzoylphcnyl] Ditellurium [Potassium Hydroxide Method]3 To 200 ml of ethanolic potassium hydroxide are added 16.5 g (48 mmol) of 2-benzoylphenyl tellurium chloride and the mixture is heated until the reddish color disappears and potassium chloride precipitates. The mixture is poured into cold water and the ditellurium compound is extracted with chloroform. The extract is dried, evaporated to dryness, and the residue is recrystallized from benzene yield 12.3 g (83%) m.p. 139°. 

Belcher et al. reported the synthesis of the strontium derivatives of tpm, ppm, and hpm by addition of the /3-diketone to an aqueous solution of the metal chloride (see later discussion for other method using MC12 salts). After adjustment of the solution pH to 7 with ammonia, the metal bis(/3-diketonate) compounds precipitate as white solids.151 The same authors have also reported the synthesis of the calcium derivatives of these three ligands by addition of the ligand to calcium hydroxide suspended in methanol. The compounds are precipitated by addition of water. The barium derivatives, however, were prepared directly by addition of the /3-diketone to an aqueous solution of barium hydroxide. The MU(L)2 2HzO (M = Ca, Sr, or Ba L = tpm, ppm, or hpm) compounds are all similar in composition. Metal hydroxide methods have also been used for the preparation of M(fod)2,152 M(hfac)2(H20) ,153 (enH2)] 5[Ba(hfac)5] ... 

For the separation and identification of Group IIA cations (Hg2+, Pb2+, Bi3+, Cu2+, and Cd2+) two, somewhat different methods are recommended. From the reagents used, these are called (a) sulphuric acid method and (b) sodium hydroxide method. 

Table V.17 Separation of Group IIA cations with the sodium hydroxide method The...

For the separation of Group II cations into Groups IIA and IIB two methods were suggested (cf. Section V.10, Tables V.14 and V.15). To separate and identify the Group IIB cations, one of the two recommended procedures must be followed, according to the method chosen in the previous step. If the ammonium polysulphide method (method a) has been followed in Section V.10, then method (a) has to be applied here. Method (b), on the other hand, has to be used if the potassium hydroxide method was followed to separate Groups IIA and IIB. 

VL11 SEPARATION OF GROUPS IIA AND IIB AND SEPARATION AND IDENTIFICATION OF GROUP IIA CATIONS When describing these separations in macro scale, two alternative methods have been suggested (see Section V.10), one being based on the use of ammonium polysulphide (see Table V.14) and the other on potassium hydroxide (Table V.15). In semimicro scale the potassium hydroxide method is more suitable and this will be presented here. This does not mean however that the ammonium polysulphide... 

If the alternative potassium hydroxide method is employed for the separation of Groups IIA and IIB, the KOH extract may contain As, Sb, Sn, Se, Te, and part of the Mo the residue may contain, in addition to HgS, PbS, Bi2S3, CuS, CdS, and PdS, the gold and platinum partly as sulphides and possibly partly in the form of the free metals. Mo is readily identified by the potassium xanthate or a-benzoin oxime test. The Au and Pt will accompany HgS after extraction with dilute nitric acid upon dissolution in aqua regia, Pt may be identified as the dimethylglyoxime complex in the presence of m hydrochloric acid after the Pb, Bi, Cu, and Cd have been removed. 

Since the P—F bonds are labile in these complexes some mixed trifluorophosphine-fluorophosphite nitrosyl complexes have been prepared by reactions with either diisopropyl-water mixtures or barium hydroxide (method F) to give the (PF20) compounds which can be alkylated. 

Hu and coworkers developed a composite hydroxide method (CHM) to symthesize highly crystallized rare earth hydroxide and oxide nanocrystals (Hu et al., 2007). The eutectic mixture of alkaline hydroxides (NaOH KOH = 51.5 48.5, m.p. 165 °C) is used as solvent and the real synthetic process is done at approximately 200 °C in a sealed vessel. The highly crystallized La(OH)3 nanobelts are obtained through this method... 

Total acidity (meq/g) and carboxyl groups (meq/g) were determined by the barium hydroxide method and the calcium acetate exchange method, respectively (X4). Phenolic hydroxyl groups (meq/g) were calculated as the difference between total acidity and carboxyl groups. These determinations were carried out under a nitrogen atmosphere to minimize absorption of carbon dioxide. 

Total acidity determined by the barium hydroxide method (14). 

Although all potentiometric methods of functional group analysis are inherently operational, the total acidity can be determined by the barium hydroxide method, if appropriate precautions are taken to remove all colored material from the reaction mixtures prior to the final titration. Any method that purportedly distinguishes between different classes of functional groups should be used with full awareness of the operational nature of the results that will be obtained. If potentiometric data are augmented with calorimetric andlor spectroscopic data, more accurate estimates of functional group concentrations may possibly be obtained. 

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