Fluoride addition

The incidence of dental caries has decreased dramatically in recent years. It has fallen to such an extent as to reduce the need for professional dental health services related to caries significantly. The cause is not clear, but water fluoridation, addition of fluoride to toothpaste, and other modes of fluoride adrninistration are generally conceded to be important contributors to the phenomenon and the American Dental Association recommends use of a fluoride toothpaste for all patients (10). 

With very electrophilic olefins, an alternative hydrogen fluoride addition process is often preferred This process, involving reaction of the olefin with fluoride ion in the presence of a proton donor, is applicable to certain perhalogen ated alkenes [/] and substrates with other electron attracting groups attached to the double bond [i5, 36] (equations 4 and 5)... 

The combination of a hydrogen fluoride addition and a chlorine-fluonne displacement converts 1,1 2,2-tetrachloroethylene-l,2 di(isocyanidedichloride)to perfluoro-A, A -dimethylethylenediamine [37] (equation 28)... 

Preparation of aryl fluorides Addition of fluoroboric acid to a solution of a diazonium salt causes the precipitation of an aryl diazonium fluoroborate. When the dry aryl diazonium fluoroborate is heated, an aryl fluoride results. This is the Schiemann reaction it is the most general method for the preparation of aryl fluorides. 

Reaction of aryl silanes with fluoride Addition of silanes to alkenes... 

Li and co-workers also reported a highly efficient conjugate addition reaction with arylsilanes as nucleophilic reagents. The reaction of 2-cyclohexenone with 4 equiv. of either diphenyldichlorosilane or phenylmethyldichlorosilane in water generated the conjugate addition product in 97% and 95% yields, respectively (Scheme 55).143 An excess of sodium fluoride additive was important in this reaction. 

Organotrialkoxysilanes (ArSi(OR)3) were used as organometallic reagents without fluoride additives (Scheme 56).144,144a ArSi(OR)3 was easy to use because of its higher air and moisture stability. Oi and co-workers believed that hydrolysis of the trialkoxysilanes to generate silanetriols was likely occurring prior to transmetallation of the cationic rhodium complex. 

The addition of fluoride to the reactive gel led to more perfect and larger crystals of known molecular sieve structures as well as new structures and compositions. The fluoride ion also is reported to serve as a template or SDA in some cases. Fluoride addition extends the synthesis regime into the acidic pH region. Synthesis in fluoride media is discussed in greater detail in references [25] and [87]. 

Banes and Hailer [81] studied the effect of fluoride addition on the size and morphology of apatite crystals in close-to-physiological conditions. These authors in particular reported that fluoride uptake was accompanied by some anisotropic growth of the apatite crystals the width and/or thickness of the crystals increased with F uptake while no noticeable change in length was observed. In addition, LeGeros et al. [66] pointed out the decrease in calcium deficiency linked to a progressive fluoride incorporation. 

Finally, other effects of fluoride addition to HA have been investigated. In particular, the electrical conductivity of HA was found to be modified with fluoride substitution, as an increase in conductivity was observed [82] for OH-F apatites where up to 50% of OH ions were replaced by F. Beyond this proportion, however, a sharp drop in conductivity was pointed out. It seems, however, difficult to... 

The combination of A/-halosuccinimides with polyfluorinated ammonium salts, in particular A/-halosuccinimide-triethylamine trisfhydrogen fluoride)42 (Method C), is convenient and effective for the halofluorination of alkenes. These easy-to-handle reagents allow work to be carried out at room temperature in conventional glass apparatus, while Olah s reagent requires polyethylene equipment. The reaction of various alkenes with A -halosuccinimide-triethylamine trisfhydrogen fluoride) in dichloromethane or diethyl ether at 0 C is complete within 3-5 hours giving the halogen fluoride addition products in 70-95% yield. 

Fluoride addition promotes the cracking (108-110) and isomerization (108, 111) activity of alumina, presumably, because of the formation of Brdnsted acid sites. In a comprehensive study of fluorided aluminas, Antipina et al. (110) demonstrated that there is a close parallelism between generation of cumene cracking activity at 430°C and surface acidity when fluoride content is increased from 0 to 7% wt (see Fig. 15). Acidity was measured by n-butylamine titration endpoints were determined by means of an arylcarbinol indicator that detected Br0nsted acids stronger than those corresponding to a pKa of — 13.3. In a separate article (112), Anti-... 

In order to make use of thorium as a nuclear resource for power generation, development of efficient separation processes are necessary to recover 233U from irradiated thorium and fission products. The THORium uranium Extraction (THOREX) process has not been commercially used as much as the PUREX process due to lack of exploitation of thorium as an energy resource (157,180). Extensive work carried out at ORNL during the fifties and sixties led to the development of various versions of the THOREX process given in Table 2.6. The stable nature of thorium dioxide poses difficulties in its dissolution in nitric acid. A small amount of fluoride addition to nitric acid is required for the dissolution of more inert thorium (181). 

Fluoridation Addition of fluoride to community drinking water. 

There are many examples of halogen fluoride addition to double bonds in steroids, but primarily the addition of bromine fluoride has been investigated (see Section 1.2.1.3.2.)- Nevertheless, there are some examples of the addition of chlorine fluoride in the preparation of fluorinated pregnane systems, " " ° ° e.g. the chlorofluorination of pregna-1.4,9(l l)-triene-3,20-dionc (5). ... 

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