S Elimination

Tp PtMejH + 02 Tp PlMe2(-0-0-H) Insertions involving CO2 are discussed in Section 12.3. 

In 16e complexes, a 2e site is asually available, except for Pd(II), and especially for Pt(U), which tend to avoid the 18e configuration. Yamamoto and co-workers found that rra/is-[PdL2Et2] complexes (L = 3° phosphine), tend to decompose by beta elimination directly from the I6e starting complex via an 18e transition stale, but [diosphine dissociation is often required for elimination in alkyls such as [PtL2Bu2J (7.7). The related metalacycle 7.8 j9-elimmates Kf-fold more slowly than 7.7, presumably because a coplanar M—C—C—H 

Grubbs and co-workers have studied the analogous nickel complexes in the presence and absence of excess phosphine and have found that di are three decomposition pathways, one for each of the different intermediates, 14e, 16e, and 18e, that can be formed (Eq. 7.36). 

Alkoxide complexes readily undergo elimination to give ketones or aldehydes, accounting for the ability of basic isopropanol to reduce many metal halides to hydrides with formation of acetone. Elimination of amides and amines to imines also occurs but tends to be slow.  

TaCl2(CH2Ph)3------ Cp TaCl CH2Ph)3------Cp Ta(=CHPh)Cl(CH2Ph) 

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K3Fe(CN)6 as a reoxidant gives higher ee s- eliminates second cycle... 

Two disadvantages are associated with the use of S-acetyl or 5-benzoyl derivatives in peptide syntheses (a) base-catalyzed hydrolysis of 5-acetyl- and 5-benzoylcys-teine occurs with /S-elimination to give olefinic side products, CH2=C-(NHPG)CO—(b) the yields of peptides formed by coupling an unprotected amino group in an 5-acylcysteine are low because of prior S-N acyl migration. ... 

Fluoride-induced /S-elimination reactions of silanes having leaving groups in the position are important processes in synthetic chemistry, as, for, example in the removal of / -trimethylsilylethoxy groups. 

The ability to promote /S elimination and the electron-donor capacity of the /3-metalloid substituents can be exploited in a very useful way in synthetic chemistry. Vinylstannanes and vinylsilanes react readily with electrophiles. The resulting intermediates then undergo elimination of the stannyl or silyl substituent, so that the net effect is replacement of the stannyl or silyl group by the electrophile. An example is the replacement of a trimethylsilyl substituent by an acetyl group by reaction with acetyl chloride. 

Some dmgs are bound to plasma proteins in blood. Plasma protein levels in blood may be decreased in the elderly, but this is most often not clinically relevant since a drug s elimination increases when the free, unbound drug concentration is enhanced (Turnheim 1998). The plasma albumin level may however be markedly decreased in elderly suffering from malnutrition or severe disease. For those patients the concentration of the free unbound drug can reach toxic levels (Waiter-Sack and Klotz 1996). 

Johanson, J. G. Yosim, S. J. Kellogg, L. G. Sudar, S. "Elimination of Hazardous Wastes by the Molten Salt Destruction Process," Proc. 8th Annu. Res. Symp. Incineration and Treatment of Hazardous Waste, EPA-600/9-83-003,... 

The good bioavailability of orally administered ciprofloxacin obviates the need for the more expensive intravenous formulation. I.v. ciprofloxacin is only given to patients who have severe sepsis or severe nausea and vomiting. Ciprofloxacin s elimination is 50% hepatic and 50% renal. Therefore, dose reduction is recommended only in case creatinine clearance drops to < 10 ml/min. Prevention of food-borne disease requires efforts at many levels. Monitoring safety of food processing, vector control, surveillance of outbreaks, education on personal hygiene and improving sanitation and access to safe water supplies are all necessary measures to reduce the incidence of GTI. 

Although the fluoride anion is not a good leaving group (because of the great strength of the C-F bond), ketones, imines and jS-fluoroesters easily afford this S-elimination reaction (Fig. 22) [77], The S-elimination process remains efficient for CF2 and CF3 compounds, while the C-F bond is stronger. Indeed, fluorine atoms render more acidic the a proton, which makes easier the formation of the anion. 

The S-elimination reactions are also very frequent and they are typical of the chemistry of fluorinated compounds. They play an important role in synthesis and also... 

Modifications of the chemical reactivity generated by the presence of fluorine atoms in a molecule are connected to three main factors the strength of the C— F bond, the electron-withdrawing character of the fluorinated substituents, and the possible loss of a fluoride ion or of HF in the processes of )S-elimination. On these bases and taking into account the ability of fluoro-substituents to sterically or electronically mimic other... 

The physician can estimate the reciprocal of the patient s elimination rate for a drug by dividing the plasma drug level by the dosing rate (i.e., the daily dose that produced that particular plasma drug level). For example, with TCAs, patients fall into three groups ... 

There is a linear relationship between dose and plasma drug levels (i.e., linear or first-order pharmacokinetics) in normal and ultrarapid metabolizers. In these individuals, the earlier equation can be used to predict the daily dose needed to produce a specific plasma drug level once TDM has been done to estimate the patient s elimination rate. In poor metabolizers, TCAs follow nonlinear pharmacokinetics (i.e., disproportionate increases in plasma drug levels with dose increases) because they lack the CYP 2D6 and must use lower affinity enzymes to metabolize these drugs. 

Two main effects occur here. First, change in the pH of urine—weak bases, such as pethidine, are more easily excreted in an acid urine while alkalinisation promotes excretion of weak acids, such as salicylates and phenobarbital. Second, drugs that compete for an active excretion mechanism will reduce each other s elimination—probenecid was used in the early days of penicillin to conserve the drug, while less desirable interactions also occur, e.g. chlorpropamide and phenylbutazone interact to give increased levels of chlorpropamide and a danger of hypoglycaemia. 

For the (S-elimination to occur smoothly the reaction mixtures must be warmed to room temperature otherwise the intermediate allylic organometallic 49 undergoes a second homologation (equation 22). 

The use of mesyl chloride for the dehydration of C-ll alcohols has already been mentioned, and mesylates can certainly be intermediates at least in the a-series. The preference for a coplanar trans arrangement is demonstrated by the well-known elimination reactions of tosylates of epimeric 20-alcohols (ref. 185, p. 616), although this does not restrict the usefulness of the reaction, and in some cases (sulfonates of 1 la-alcohols, for example) c/s-elimination occurs (ref. 216, p. 293 ref. 224, 225, 226). 

Volume of distribution and clearance are both properties of a drug. These two properties determine a drug s elimination rate constant and half-life (Equation 7.12). 

The instantaneous velocities of the spheres after their creation are x° and x2 and the temporal terms are vanishingly small when 10-12 s. Eliminating the exponential terms and using the expansions /<= mxm2/(mx + m2), d12 x° + x2, and p = rxr2l... 

Scheme 2 /S-Elimination starting from C6-aldehyde structures in cellulose...

Scheme 5 Cleavage of the glycosidic bond by /S-elimination starting from C3-keto structures along the cellulose chain...

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