Graphite reagents

Zinc and Mercury. - New methods for the preparation of reactive forms of zinc broaden the synthetic applications of this metal. The use of a Zn/Ag- graphite reagent, prepared from CgK and ZnC /AgOCOCHg, allows the Reformatsky reaction to be carried out efficiently at low... 

A paper describing the methylenation of aldonolactones using dicyclopentadienyldimethyl titanium as a more stable alternative to the Tebbe reagent has been presented (Scheme 9). Also described is the use of the zinc-silver/graphite reagent for effecting a Reformatsky-like reaction on aldonolactones with ethyl bromoacetate... 

Finally, analytical methods can be compared in terms of their need for equipment, the time required to complete an analysis, and the cost per sample. Methods relying on instrumentation are equipment-intensive and may require significant operator training. For example, the graphite furnace atomic absorption spectroscopic method for determining lead levels in water requires a significant capital investment in the instrument and an experienced operator to obtain reliable results. Other methods, such as titrimetry, require only simple equipment and reagents and can be learned quickly. 

It is used as a fluorinating reagent in semiconductor doping, to synthesi2e some hexafluoroarsenate compounds, and in the manufacture of graphite intercalated compounds (10) (see Semiconductors). AsF has been used to achieve >8% total area simulated air-mass 1 power conversion efficiencies in Si p-n junction solar cells (11) (see Solarenergy). It is commercially produced, but usage is estimated to be less than 100 kg/yr. 

Two colorimetric methods are recommended for boron analysis. One is the curcumin method, where the sample is acidified and evaporated after addition of curcumin reagent. A red product called rosocyanine remains it is dissolved in 95 wt % ethanol and measured photometrically. Nitrate concentrations >20 mg/L interfere with this method. Another colorimetric method is based upon the reaction between boron and carminic acid in concentrated sulfuric acid to form a bluish-red or blue product. Boron concentrations can also be deterrnined by atomic absorption spectroscopy with a nitrous oxide—acetjiene flame or graphite furnace. Atomic emission with an argon plasma source can also be used for boron measurement. 

Aluminium fluoride (anhydrous) [7784-18-4] M 84.0, m 250°. Technical material may contain up to 15% alumina, with minor impurities such as aluminium sulfate, cryolite, silica and iron oxide. Reagent grade AIF3 (hydrated) contains only traces of impurities but its water content is very variable (may be up to 40%). It can be dried by calcining at 600-800° in a stream of dry air (some hydrolysis occurs), followed by vacuum distn at low pressure in a graphite system, heated to approximately 925° (condenser at 900°) [Henry and Dreisbach J Am Chem Soc 81 5274 1959]. 

Xenon difluoride [55], xenon difluoride complexed with dialkyl sulfides [59], and xenon difluoride intercalated with graphite [90] are all effective reagents for the fluonnalion of acids, enolates, or enols (Table 2)... 

For the synthesis of coumarins, the Pechmann reaction [145] is one of the most popular synthetic routes. As the reaction is conventionally carried out at high temperature, two microwave-assisted versions have been recently described. Besson and co-workers described the cyclocondensation of different m-amino phenols 226 with /1-ketoesters 227 on graphite/montmorillonite KIO support (Scheme 83). The use of graphite was crucial in the development of the reaction conditions. In fact, microwave irradiation of the reagents using different conditions gave poor results in terms of yields and purity. The optimized conditions, using a monomode microwave system, employed... 

Graphite acid salts have been considered in terms of possible practical applications. Their potential as useful electrodes in high-energy-density batteries has been reviewed (AS), as well as their potential usefulness as chemical reagents (B14). 

In order to derive a quantitative relation between emission Intensity as measured by EMI and actual metal content, cell samples were subjected to graphite furnace atomic absorption (GFAA) analysis (14). Atomic absorption experiments were performed both on cells which had been stained with a fluorescent reagent and on cells not exposed to a lumlnophore. After EMI analysis, 50 fiL of cell suspension were withdrawn from the 0.30 mL of sample used for EMI and were digested In 150 iiL of concentrated HNO3 for 90 minutes at 85° . These solutions were then diluted to 1/10 of their concentration with deionized water, and the 150 liL of these diluted... 

Boron nitride may be obtained in three primary crystalline modifications (2) a, j3, and y. The most commonly encountered a form has a graphitic structure (hexagonal cell, a = 2.504 A, c = 6.661 A). For many years, this modification has been prepared from combinations of cheap boron and nitrogen containing reagents, e.g. B(0H)3 and (NH2)C0, B(0H)3, C and N2 or KBH4 and NH4C1 (3-5). More... 

Since the specific surface area of modem graphite materials is Sv 104 -r- lO m 1 (Sm 10-2 - 104m2g 1 ), it is almost always possible to make an electrode characterized by A > 1 from a mixture of a carbon material and a solid reagent. 

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