Thallium reactions

What procedures arc available for preparing a phenol Answer Procedure XIII-1 involving a thallium derivative and procedure XIII-5 which involves the use of a diazonjum salt. Since willi alkyl groups the thallium reaction goes exclusively para, let us use procedure XIII-1. This will require tire use of /-butylbenzcnc which is a permitted starting material. 

Stereoselective cis-dihydroxylation of the more hindered side of cycloalkenes is achieved with silver(I) or copper(II) acetates and iodine in wet acetic acid (Woodward gly-colization J.B. Siddall, 1966 L. Mangoni, 1973 R. Criegee, 1979) or with thallium(III) acetate via organothallium intermediates (E. Glotter, 1976). In these reactions the intermediate dioxolenium cation is supposed to be opened hydrolytically, not by Sn2 reaction. 

Thallium(III) acetate reacts with alkenes to give 1,2-diol derivatives (see p. 128) while thallium(III) nitrate leads mostly to rearranged carbonyl compounds via organothallium compounds (E.C. Taylor, 1970, 1976 R.J. Ouelette, 1973 W. Rotermund, 1975 R. Criegee, 1979). Very useful reactions in complex syntheses have been those with olefins and ketones (see p. 136) containing conjugated aromatic substituents, e.g. porphyrins (G. W. Kenner, 1973 K.M. Smith, 1975). 

Ketones are rearranged oxidatively by reaction of the corresponding enols with thallium(III), e.g. to yield pyrroleacetic acids from acetyl pyrroles (G.W. Kenner, 1973 B W. Rotermund, 1975). 

Thallation of aromatic compounds with thallium tris(trifluoroacetate) proceeds more easily than mercuration. Transmetallation of organothallium compounds with Pd(II) is used for synthetic purposes. The reaction of alkenes with arylthallium compounds in the presence of Pd(Il) salt gives styrene derivatives (433). The reaction can be made catalytic by use of CuCl7[393,394], The aryla-tion of methyl vinyl ketone was carried out with the arylthallium compound 434[395]. The /9-alkoxythallium compound 435, obtained by oxythallation of styrene, is converted into acetophenone by the treatment with PdCh[396]. 

In the total synthesis of the naturally occurring big molecule of palytoxin, which has numerous labile functional groups, this coupling is the most useful for the creation of E, Z-conjugated diene part 653. In this case, thallium hydroxide as a base accelerates the reaction 1000 times more than KOH[523]. Even TECOj can be used instead of a strong base in other cases[524]. 

Reference Electrodes and Liquid Junctions. The electrical cincuit of the pH ceU is completed through a salt bridge that usually consists of a concentrated solution of potassium chloride [7447-40-7]. The solution makes contact at one end with the test solution and at the other with a reference electrode of constant potential. The Hquid junction is formed at the area of contact between the salt bridge and the test solution. The mercury—mercurous chloride electrode, the calomel electrode, provides a highly reproducible potential in the potassium chloride bridge solution and is the most widely used reference electrode. However, mercurous chloride is converted readily into mercuric ion and mercury when in contact with concentrated potassium chloride solutions above 80°C. This disproportionation reaction causes an unstable potential with calomel electrodes. Therefore, the silver—silver chloride electrode and the thallium amalgam—thallous chloride electrode often are preferred for measurements above 80°C. However, because silver chloride is relatively soluble in concentrated solutions of potassium chloride, the solution in the electrode chamber must be saturated with silver chloride. 

Titration Indicators. Concentrations of arsenic(III) as low as 2 x 10 M can be measured (272) by titration with iodine, using the chemiluminescent iodine oxidation of luminol to indicate the end point. Oxidation reactions have been titrated using siloxene the appearance of chemiluminescence indicates excess oxidant. Examples include titration of thallium (277) and lead (278) with dichromate and analysis of iron(II) by titration with cerium(IV) (279). 

Thallic oxide can be prepared by reaction of thallium with oxygen or hydrogen peroxide and an alkaline thallium(I) solution. However, it is more easily made from the oxidation of thaHous nitrate by chlorine ia aqueous potassium hydroxide solution. It is insoluble in water but dissolves in carboxyUc acids to give carboxylates. 

A mild and effective method for obtaining N- acyl- and N- alkyl-pyrroles and -indoles is to carry out these reactions under phase-transfer conditions (80JOC3172). For example, A-benzenesulfonylpyrrole is best prepared from pyrrole under phase-transfer conditions rather than by intermediate generation of the potassium salt (81TL4901). In this case the softer nature of the tetraalkylammonium cation facilitates reaction on nitrogen. The thallium salts of indoles prepared by reaction with thallium(I) ethoxide, a benzene-soluble liquid. 

This reaction avoids the use of toxic thallium compounds. 

Trifluoroacetates of silver, mercury(II), thallium(lll), lead(IV), and lodme(III) are synthetically valuable reagents that combine the properties of strong electrophiles, oxidizers, and Lewis acids Furthermore, trifluoroacetate anions are stable to oxidation, are weak nucleophiles, and usually do not cause any contamination of the reaction mixture... 

Several derivatives of indolo[3,2-fi]carbazole, such as the system 185, have been claimed to arise from the reaction of suitably substituted simple indoles on treatment with thallium triacetate in acetic acid. A compound having the purported structure of 185 was thus isolated when 2,3-dimethylindole was used as the substrate [78UC(B)422]. Many years later, it was demonstrated that this product is in fact a derivative of indolo[2,3-c]carbazole (cf. Section VI) (99T12595). 

The Teijin oxychlorination, on the other hand, is considered a modern version of the obsolete chlorohydrin process for the production of ethylene oxide. In this process, ethylene chlorohydrin is obtained by the catalytic reaction of ethylene with hydrochloric acid in presence of thallium(III) chloride catalyst ... 

Catalyst regeneration occurs by the reaction of thallium(I) chloride with copper(II) chloride in the presence of oxygen or air. The formed Cu(I) chloride is reoxidized by the action of oxygen in the presence of HCI ... 

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