Type B reactions

Figure 223. Types of chemical heat pump (a) reaction phase change batch type, (b) reaction reaction batch type, (c) reaction separation work continuous type...

Type (b) reaction on this rearranged cation (16) will yield more propene (15), while type (a) reaction with water will yield propan-2-ol... 

These results clearly show that in type B reactions the electrooxidation pattern is remarkably different from that of the corresponding monoolefin. The types A and B are summarized schematically in equation 14. 

In type A reactions one electron is removed from one of the two double bonds to form a cation radical, and allylic substitution and oxidative addition take place as the following reactions. On the other hand, in type B reactions the initial electron transfer from the double bond is accompanied by a transannular reaction between the two double bonds. 

None of these factors alone should be considered to indicate a Type B reaction, and any taken singly can be associated with a Type A reaction. This list should be taken as a starting point in determining if an adverse drug reaction is a type of drug allergy. The following are additional considerations. 

Although all of the reported Rh-catalyzed reactions of allenynes were of type A, an Ir catalyst resulted in a different regioselectivity. That is, when allenynes with two substituents on the allene terminus were used under a low partial pressure of CO, the type B reaction proceeded exclusively such that bicyclic cyclopentenones with an aLkylidene substituent were obtained (Scheme 11.22) [34]. However, when [RhCl(CO)(PPh3)2] was used as a catalyst under the same reaction conditions in place of [IrCl(CO)(PPh3)2], the type A reaction was predominant These results imply that the metal centers of the catalysts control the regioselectivity of two ole-finic moieties of allene to some extent... 

Pyridine and its congeners undergo reaction with hydroxide ions by paths A (Chapter 2.06), B, C (Chapter 2.06), D and E (Section 2.05.5). The most important types of reaction with hydroxide are B and D these will be described here considering Type B reactions first. 

A. Type-B Reactions Rearrangements of the Blcyclic Photoproducts of Type-A Processes... 

Reactions of type (a) for Na, K, Rb, and Cs can attain equilibrium, and those constants were calculated. Calculations are in good agreement with experimentally determined values. No calculations could be carried out for type (b) reactions. Only for Mg(I03)2 have enthalpy increments above 298 K been measured, but in this case S°(298 K) is not known. There are no experimental studies. For reactions of type (c) only the calculation for Ca could be done since no S°(298 K) values for the periodates of Li, Ba, and Sr are available. 

Solvolysis rates of t-butyl-dimethylsulfonium salts decrease with increasing solvent polarity [710]. Analogously, the rate of solvolysis of triethyloxonium salts in ethanol/water mixtures decreases with increasing water content [490]. Solvolysis rates of A-t-alkylpyridinium salts such as 1-(1-methyl-l-phenylethyl)pyridinium perchlorate are almost independent of solvent polarity, whereas A-s ec-alkylpyridinium salts exhibit small decreases in rate with increasing solvent polarity [710]. The non-creation of charge in the activation process of these type (b) reactions much reduces the influence of solvent polarity on rate cf. Table 5-4. 

Hydrazone cyclization and hydroalkylation [138-140] are rare examples of reactions conducted on a preparative scale, since the products were isolated in milligram amounts and not just identified in solution. As already mentioned in Section 6.2.5, photocorrosion of the semiconductor photocatalyst often prevents its use in preparative chemistry. This is very true also for colloidal semiconductors although the pseudo-homogeneous nature of their solutions allows one to conduct classical mechanistic investigations, until now they were too labile to be used in preparative chemistry [107, 141, 142]. In contrast to the above-mentioned reactions, in recent years we have isolated novel compounds on a gram-scale employing photostable zinc and cadmium sulfide powders as photocatalysts [97, 107, 143-145]. During this work we found also a new reaction type which was classified as semiconductor photocatalysis type B [45]. In contrast to type A reactions, where at least one oxidized and one reduced product is formed, type B reactions afford only one unique product, i.e., the semiconductor catalyzes a photoaddition reaction (see below). 

A) reactions. Other drugs, e.g. antimicrobials, have a tendency to cause allergy and may lead to bizarre (type B) reactions. Ingredients of a formulation, e.g. colouring, flavouring, sodium content, rather than the active drug may also cause adverse reactions. 

As the example of the type [B] reaction, the reports by Holzapfel et al. and Chiara et al. who independently reported this type of reaction are described. Initially, Holzapfel et al. reported the Sml2-mediated radical cyclization of the ring-opened hex-5-enals [XXI] derived from pyranoses [XIX] via the step of the reductive elimination of C6 iodopyranose derivatives [XX] with active Zn [217] (O Fig. 15, Eq. (1)). Afterwards, they also reported the one-pot Sml2-... 

Adverse events are sometimes termed type A (usually pharmacologically predictable, relatively frequent, seldom fatal and usually identified during clinical trials) or type B (unpredictable idiosyncratic reactions which are usually infrequent but can be very serious or fatal) (Rawlins and Thompson, 1977 Venning, 1983). Postmarketing ADR monitoring usually identifies the more serious, type B reactions. The sample size needed in clinical trials to detect differences between an incidence rate of 1/10 000 and 2/10 000 is about 306 000 patients (e.g. for a placebo comparison of chloramphenicol-induced aplastic anemia, which occurs in 1/30 000 Lasagna, 1983). Clinical trials at this scale are simply impractical. 

In this section, our discussion focuses on the type A pathway. Because modification of an existing carbene ligand to produce a new carbene is an example of a type of reaction carbenes may undergo, we will postpone discussion of type B reactions until Section 10-3. 

Type B reactions are more common than type A reactions, but are less severe (3 to 5 per 100 treatments vs. 5 per 100,000 treatments). Chest and back pain are the most frequently reported symptoms and may be noted within minutes of the start of dialysis or delayed (up to 1 to 2 hours). Complement activation has been suggested as the initiating event. Although no specific treatment is warranted and the patient can continue with dialysis treatment, the patient may be switched to a different dialyzer and/or put on a reprocessing program because this may minimize the occurrence of this reaction in the future. ... 

When the copper-catalysed reactions (type A and type B) were performed in the cavity of an ESR spectrometer, the presence of phenyl radicals was detected by way of their spin adducts with 2-methyl-2-nitrosopropane and with 2,4,6-tribromonitrosobenzene.98 In view of these observations, Dodonov et al. suggested that a free-radical mechanism was involved in both reaction types, A and B, and explained the formation of the hypervalent copper (HI) intermediate. (Scheme 6.23) The copper (HI) intermediate is formed by two consecutive one-electron oxido-reduction elementary steps. The copper (1) catalytic species is first oxidised to a copper(Il) species which is then oxidised by a phenyl rascal to the active copper (HI) intermediate. This hypervalent species then undergoes a ligand coupling reaction with the substrate, either hydroxylic or an amino derivative. In the type B reaction, the in situ generated phenylcopper (III) diacetate reacts with the substrate to eventually afford the O- or the iV-phenyl derivative. 

Cyclic enones, such as substituted cyclohex-2-enones or cyclohexa-2,5-diones, also undergo sigmatropic photorearrangement to form bicyclo[3.1.0]hexanones (lumiketones) or bicyclo[3.1.0]hex-3-en-2-ones, respectively, for which both concerted and stepwise (biradical) reaction mechanisms have been proposed.640,641,770 For example, a [l,2]-shift concurrently with the ring contraction (termed the type A reaction) is observed upon irradiation of the methylphenyl derivative 159 in polar solvents, whereas phenyl migration (termed the type B reaction) predominates in nonpolar solvents (Scheme 6.70).771,772 The reactions are believed to proceed via both the n,n and n,Tt triplet ketone states. In the presence of alkenes, cyclic enones may readily undergo a competitive photocycloaddition reaction (Section 6.1.5). 

Enzymes which catalyze the reaction type (a) include phosphodiesterases, phospholipases (C and D), nucleotidyl transferases, nucleases, and pyrophos-phokinases. The type (b) reaction involves mainly phosphokinases and phos-phomutases. The hydrolysis of phosphomonoesters (reaction type c) is catalyzed by phosphatases, nucleotidases, ATPases, and so on. Most phosphatases also catalyze the phosphoryl transfer reaction, type (b), if an alcohol is used as an acceptor. 

ADRs are often classified into two major sorts so called Type A and Type B reactions. Type A adverse reactions are those which may be anticipated from the nature of the treatment (perhaps due to knowledge of class effects or mechanisms of action) and are dose-dependent. Type B adverse reactions are those which are unpredictable from background knowledge. They are usually a form of hypersensitivity or immunological reaction peculiar to the individual and may occur even with very small doses. They may be caused by the drug itself or by metabolites. Type B reactions are usually rarer and more serious than type A reactions. 

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