Scaling reduction

For most laboratory scale reductions of aldehydes and ketones catalytic hydro genation has been replaced by methods based on metal hydride reducing agents The two most common reagents are sodium borohydride and lithium aluminum hydride... 

On a laboratory scale reduction of KCIO3 with moist oxalic acid generates the gas suitably diluted with oxides of carbon ... 

It should be remarked here that trimethylsilane 84 a or triethylsilane 84 b and most other known silanes, for example tetramethyldisiloxane 1788, are quite expensive for any large-scale reduction, whereas the subsequently described poly-methylhydrosiloxane 1856 (cf. reductions of an azide moiety in 1855 and a carbo-benzoxy moiety in 1859) is available as large-scale orders for ca 15 kg , which is only a fraction of the cost of any other silane. 

The mass-related metrics shown in Figure 5.11 indicate that the amount of a substrate (see also byproduct formation), an auxiliary material for reaction, and of a solvent have to be reduced. The detailed view of the mass indices of the pilot scale, for example, the segments Substrates and Aux (R) and the size of segments Substrates (excess) and Aux (R) of the environmental factor E, deliver the information listed in Table 5.2 108% base and 162% auxiliary (R) are used. The measure to increase base addition for recycling purposes was successful at the expense of 193% base, much auxiliary material Aux (R) was saved in operation scale (reduction from 162% to only 13%). This leads to an overall... 

The Birch-type electrochemical reduction (460) (461) has been shown to proceed through the action of tetra-butylammonium amalgam in the steps (460)— (462)— (463), in contrast to a direct electron transfer from the electrode to the aromatics (Scheme 158) [548]. The preparative-scale reduction of anisole, of l,2,3,4-tetrahydro-6-methoxynaphthalene, and several aromatic steroids is performed in an H20-Bu4N0H-(Hg) system. The unique aspect of the reduction is the proposed formation of a tetrabutylammo-nium amalgam complex, BU4N (Hg) (465)... 

Preparative scale reduction of cyclohexanone affords principally the tail-to-tail hydrodimer 23 and some of the hcad-to-tail isomer 24 [93]. The proportions vary with pH, and no head-to-head pinacol has been isolated. Both meso- and ( )-forms... 

Ring opening is observed during the preparative scale reduction of 1-cyclo-propylethyidenemalononitnles where the carbon-carbon bond cleavage occurs with preferential formation of the most substituted carbon radical intermediate [111]. Cleavage of the carbon-carbon bond is also activated by four carbomethoxy sub-... 

The carbon-nitrile bond in cyanoalkanes is cleaved by reduction at very negative potentials. This is the route for decomposition of acetonitrile at tlie limit for its use as an aprotic solvent in electrochemistry [114, 115]. Preparative scale reduction of cyanoalkanes is best carried out in anhydrous ethylamine containing lithium chloride as supporting electrolyte and gives 60-80 % yields of the alkane plus cyanide ion. 

Alkyl alkanoates are reduced only at very negative potentials so that preparative scale experiments at mercury or lead cathodes are not successful. Phenyl alkanoates afford 30-36% yields of the alkan-l-ol under acid conditions [148]. Preparative scale reduction of methyl alkanoates is best achieved at a magnesium cathode in tetrahydrofuran containing tm-butanol as proton donor. The reaction is carried out in an undivided cell with a sacrificial magnesium anode and affords the alkan-l-ol in good yields [151]. In the absence of a proton donor and in the presence of chlorotrimethylsilane, acyloin derivatives 30 arc formed in a process related to the acyloin condensation of esters using sodium in xylene [152], Radical-anions formed initially can be trapped by intramolecular addition to an alkene function in substrates such as 31 to give aiicyclic products [151]. 

Preparative scale reduction of oximes at a mercury or lead cathode in acid solution has been used in the conversion of the carbonyl function to amine. Originally, 30-50% sulphuric acid was used as solvent [195] but ethanol with dilute hydrochloric acid is usually satisfactory. Aliphatic and aromatic oximes give amines in 64-86% yields [196]. Aromatic ketoximes are also reducible in alkaline solution and acetophenone oxime has been converted to 1-phenylethylamine in a tri-potassium orthophosphate solution [197], The reduction of oximes in acid solution is tolerant of many other substituents as indicated by a number of examples [198, 199, 200. Phenylglyoxa monoxime in acid solution is however reduced at both the carbonyl and the oxime centres by sodium amalgam to yield 2-amino-1-phenylethanol [201]... 

Large-scale reduction of phenylhydrazones at mercury or lead in ethanolic hydrochloric acid or 30-50% sulphuric acid results in cleavage of the nitrogetr-... 

Preparative scale reduction of nitramines and nitrosamines in acid solution is a convenient route to substituted hydrazines. Early workers used a cathode of tinned copper [120], More recently mercury has been employed as cathode material, although tin would probably be equally suitable. Nitrosamines are conveniently reduced in dilute hydrochloric acid and evaporation of the electrolyte at the end of the reaction affords the hydrazine hydrochloride [121]. Some nitroso compounds are unstable to these acidic conditions. In the case of N-nitrosoindoles, this problem has been overcome in an ingenious manner [122]. The nitroso compound and aqueous sulphuric acid are mixed just prior to reaction and then forced through a porous cathode of bronze coated with mercury at such a rate that the reduction is completed in one pass through the cathode. Other workers have overcome the instability of N-benzyl-N-nitrosoanthraniiic acid towards acid by working in an acetate buffer at below room temperature [123],... 

Aluminum amalgam reduces aUphatic 53 aromatic nitro compounds to hydroxylamines in consistently good yields (equation 51) and this can be the method of choice for large-scale reductions. 

In various types of bacteriological cellulose fermentations, large-scale reduction of sugar takes place. Relevant facts as well as the older literature can be found in an article by Neuberg and Cohen, while the metabolism of wood-destroying fungi is treated by Nord and Sciarini. Butyric acid and other products of reduction probably are formed as in butyl fermentations. Definite results with pure cultures are hardly available from most of the early papers. 

Reduction of acid chlorides to aldehydes. Two laboratories12 have published details for this reduction. One difficulty is the large quantities of reagent needed for preparative-scale reactions. For large-scale reductions the Rosenmund reaction is preferable. 

Stimulate the development and implementation of technologies and processes that result in reduced pollution. Numerous pollution prevention opportunities exist in manufacturing, mining, agricultural, and service processes. This goal addresses the need to focus research activities on these processes to enable broad-scale reduction in pollution generation. 

Transfer hydrogenation of ketones catalyzed by a transition-metal complex or a main group-metal alkoxide is a useful method to produce secondary alcohols. Pure organic compounds such as 2-propanol [2,281,282] and formic acid [283] are preferably used as hydrogen donors in place of hydrogen gas. This method is convenient for a small- or medium-scale reduction... 

Based on the precedented reduction of 2//-dihydropyrones,86 the combination of Lewis acid and hydride source exemplified by Et3SiH/BF3 seemed ideally suited to our needs (Scheme 9). While (+)-artemisinin 1 could not be reduced directly to 10-deoxoartemisinin 108 with Et3SiH/BF3, dihydroartemisinin (175, R = H) was smoothly converted at low temperature to desired tetrahydropyran 108 in 96% yield. Further, this method was insensitive to scale being readily accomplished on the gram or milligram level. It was also found that small scale reductions could be more conveniently conducted utilizing diisobutylaluminum hydride in place of sodium borohydride. As applied to the problematical case, it was found that lactone 125 could be reduced to lactol and thence 115 as outlined in Scheme 3 in excellent yield. Furthermore, the yield for the conversion of lactone 45 into 9-butyl-10-deoxoartemisinin 112 could be similarly improved from 58 to 90%. 

The eigenvalues of the first-principles Hamiltonian (19) for all RE ions are overestimated with respect to the eigenvalues of the semiempirical Hamiltonian (1) by 20-30%, as we have seen in the case of Pr3"1" in the previous section. This enabled us to introduce the ion-dependent scaling (reduction) factor by the following equation ... 

FIGURE 17.11 Effect of protease exposure time on visual scaling. Mean visual scaling reduction is the reduction in visual scaling from baseline after exposure to 0.5% bovine pancreatic chymotrypsin (43 GU/ml). From El-Kadi, K., Rawlings, A. V., Feinberg, C., Nunn, C., Battaglia, A., Chandar, P., Richardson, N., Sabin, R., and Pocalyko, D. Arch. Dermatol. Res., 293, 500-507, 2001. 

Besides the benefits of scale reduction and trypsin immobilization, microsystem technology has other advantages to offer. For example, Ekstrom et al. [345] described a device that integrated an enzyme microreactor with a sample pretreatment robot and... 

One of the earliest reported preparations of the requisite glycosidation precursor 5-deoxy-l,2,3-tri-0-acetyl-p-D-ribofuranoside (17) was published by Kissman and Baker in 1957.23 D-Ribose was heated at reflux in a methanol/acetone mixture in the presence of concentrated HCI to provide methyl 2,3-O-isopropylidene-D-ribofuranosidc (21), which was in turn converted to the corresponding 5-O-mesyl ribofuranoside 22 with methanesulfonyl chloride in pyridine in 63% yield. The sulfonate moiety of 22 was then displaced with sodium iodide in refluxing DMF to provide 5-deoxy-5-iodo derivative 23 in 76% yield on a multigram scale. Reductive dehalogenation of 23 was accomplished under heterogeneous catalytic hydrogenation conditions to provide the reduced 2,3-0-protected intermediate 24 in 56% yield, which was subjected to hydrolysis conditions in... 

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