Commercially available initiators

There are many different molecular mechanics force fields available. Many of them were originally developed in academic laboratories to solve specific problems. For example, some were designed to handle small molecules while others were developed to deal with protein structures. Today, the original demarcation between macromolcules and small molecules has become blurred, and they now are commercially available. Initially, many molecular mechanics programs were distributed at nominal costs, but due to the lack of federal funding for most molecular mechanics... 

Unless a substrate or reagent contains an acidic or basic site, the conditions for most radical reactions are neutral. Thus, ionic side reactions such as base-catalyzed epimerization are rarely a problem. While radical reactions are typically conducted at temperatures above ambient, this is often solely for experimental convenience most commercially available initiators require heating to generate radicals. Many radical reactions should succeed at lower temperatures provided that the chain is maintained (in chain methods) or that the rate of generation of radicals is sufficiently rapid (in nonchain methods). Low temperature initiators are available.30,31... 

Recently, a potent inhibitor of Bcl-xL was discovered after applying the SAR by NMR technique to an initial hit from an NMR-based screen.1141 We applied NOE matching to one of the commercially available initial hits [4-fluorobiphenyl-4-carboxylic acid 7, Kd = 300 30 pM],... 

The following catalytic cycle is postulated.14 The (commercially available) initiating catalyst 33 is transformed into the propagating catalyst 41 running the following mechanism one time. 41 then enters the cycle by loss of one phosphine ligand. Henceforth 42 catalyzes the transformation of 10 to 11. 

As there are no suitable organometallic precursors commercially available, initial work dealt with the synthesis of such a precursor [4]. 2,5-Bis(rbutyl)-2,5-diaza-l-germa-cyclopentane is a monomeric solid with a melting point of 45 °C and a sufficient vapour pressure of 0.40 mbar at 40 °C to allow its introduction into the CVD reactor. For the details about the synthesis and properties of this precursor we refer to a recent paper [4]. The present work deals with the investigation of the thermal decomposition of the precursor, the deposition of amorphous germanium (a-Ge) and the characterization of the deposited thin films. Finally some data should try to give some understanding about the deposition mechanism. 

Simple synthetic protocols for carbon-carbon and carbon-nitrogen bond formation using an air-stable palladium catalyst bearing an NHC ligand have been presented. The (IPr)Pd(allyl)Cl catalyst can be prepared on a large scale in high yield, better yet it is commercially available. Initial catalyst testing was performed on a small scale but the ease with which the described chemistry can be scaled up has now been shown. 

There were limited commercially available initiators/control agents for polymerization of high molecular weight (meth)acrylates (25)... 

Another advantage of ATRP is a multitude of commercially available initiators. Nearly all compounds with halogen atoms activated by the presence of 3-carbonyl, phenyl, vinyl or cyano groups have been used as efficient initiators. Also compounds with a weak halogen-heteroatom bond can be used, such as sulfonyl halides [31]. Small molecule initiators can carry additional functionalities, a few examples are shown in Scheme 9, the functionality is incorporated at the residual chain end. 

In this example, the initiating alkoxy radical abstracts a hydrogen from sulfur to yield CH3CH2S , which then attacks the double bond. Bis(l,l-dimethylethyl) peroxide (di-tert-butyl peroxide) and dibenzoyl peroxide are commercially available initiators for such radical addition reactions. 

Some commercial substrates were/are also available for SERS but to date none of them have become universal substrates for SERS analytical applications. Klarite substrates designed from silicon regular inverse pyramidal patterns coated with Au layer (Pemey et al. 2007) are one example. This substrate had been commercially available initially by a spin-off enterprise of the University of Southampton and then marketed by the Renishaw, Inc., Renishaw Diagnostics. Although the Klarite substrates do not provide high EF, the spectral reproducibility is sufhcient for some sensing applications. 

The above-described ATRP mechanism is identical either if polymerization occurs in bulk or if started from a surface (i.e., surface-initiated). Many commercially available initiators (e.g., alkyl halides) can be used, as long as they present a weak halogen-heteroatom bond. The initiator will provide the polymer a surface with simple halogen as end groups, which is easily converted into useful functionalities. The transition metal complexes used (Ru, Cu, Fe, Ni, among others) are responsible for the conversion into useful functionalities, removing the halides from the polymer surface. The surface is then ready for polymerization [131]. 

Introduction and Commercial Application The production decline period for a field is usually defined as starting once the field production rate falls from its plateau rate. Individual well rates may however drop long before field output falls. This section introduces some of the options that may be available, initially to arrest production decline, and subsequently to manage decline in the most cost effective manner. 

Solution Polymerization. Plant scale polymerizations ia water are conducted either adiabaticaHy or isotherm ally. Molecular weight control, exotherm control, and reduction of residual monomer are factors which limit the types of initiators employed. Commercially available high molecular weight solution polyacrylamides are usually manufactured and sold at about 5% soHds so that the viscosities permit the final product to be pumped easily. 

Other Borohydrides. Potassium borohydride was formerly used in color reversal development of photographic film and was preferred over sodium borohydride because of its much lower hygroscopicity. Because other borohydrides are made from sodium borohydride, they are correspondingly more expensive. Generally their reducing properties are not sufficiently different to warrant the added cost. Zinc borohydride [17611-70-0] Zn(BH 2> however, has found many appHcations in stereoselective reductions. It is less basic than NaBH, but is not commercially available owing to poor thermal stabihty. It is usually prepared on site in an ether solvent. Zinc borohydride was initially appHed to stereoselective ketone reductions, especially in prostaglandin syntheses (36), and later to aldehydes, acid haHdes, and esters (37). 

Borabicyclo [3.3.1] nonane [280-64-8], 9-BBN (13) is the most versatile hydroborating agent among dialkylboranes. It is commercially available or can be conveniendy prepared by the hydroboration of 1,5-cyclooctadiene with borane, followed by thermal isomerization of the mixture of isomeric bicychc boranes initially formed (57,109). 

Diperoxyketals. Some commercially available di(/ f2 -alkylperoxy)ketals and their corresponding 10-h half-life temperatures (deterrnined in dodecane) are hsted in Table 5 (39). Diperoxyketals thermally decompose by cleavage of only one oxygen—oxygen bond initially, usually foUowed by P-scission of the resulting alkoxy radicals (40). For acychc diperoxyketals, P-scission produces an alkyl radical and a peroxyester. 

Diall l Peroxides. Some commercially available diaLkyl peroxides and their corresponding 10-h half-life temperatures in dodecane are Hsted in Table 6 (44). DiaLkyl peroxides initially cleave at the oxygen—oxygen bond to generate alkoxy radical pairs ... 

GeneraHy, the commercially available azo initiators are of the symmetrical azonittile type ... 

Commercially available MEKP formulations are mixtures of the dihydroperoxide (1), where X = OOH R = H, R = methyl, and R = ethyl (2,2-dihydroperoxybutane [2625-67 ]) and dialkyl peroxide (2), where X = OOH, Y = OOH, R = methyl, and R = ethyl (di(2-hydroperoxy-2-butyl) peroxide [126-76-1J). These formulations are widely used as free-radical initiators in the metal-promoted cure of unsaturated polyester resins at about 20°C. 

Buffers are frequently added to emulsion recipes and serve two main purposes. The rate of hydrolysis of vinyl acetate and some comonomers is pH-sensitive. Hydrolysis of monomer produces acetic acid, which can affect the initiator, and acetaldehyde which as a chain-transfer agent may lower the molecular weight of the polymer undesirably. The rates of decomposition of some initiators are affected by pH and the buffer is added to stabilize those rates, since decomposition of the initiator frequently changes the pH in an unbuffered system. Vinyl acetate emulsion polymerization recipes are usually buffered to pH 4—5, eg, with phosphate or acetate, but buffering at neutral pH with bicarbonate also gives excellent results. The pH of most commercially available emulsions is 4—6. 

Complexation of the initiator and/or modification with cocatalysts or activators affords greater polymerization activity (11). Many of the patented processes for commercially available polymers such as poly(MVE) employ BE etherate (12), although vinyl ethers can be polymerized with a variety of acidic compounds, even those unable to initiate other cationic polymerizations of less reactive monomers such as isobutene. Examples are protonic acids (13), Ziegler-Natta catalysts (14), and actinic radiation (15,16). 

Physical properties of some commercially available polyamines appear in Table 1. Generally, they are slightly to moderately viscous, water-soluble Hquids with mild to strong ammoniacal odors. Although completely soluble in water initially, hydrates may form with time, particularly with the heavy ethyleneamines (TETA, TEPA, PEHA, and higher polyamines), to the point that gels may form or the total solution may soHdify under ambient conditions. The amines are also completely miscible with alcohols, acetone, benzene, toluene and ethyl ether, but only slightly soluble in heptane. 

The direct combination of selenium and acetylene provides the most convenient source of selenophene (76JHC1319). Lesser amounts of many other compounds are formed concurrently and include 2- and 3-alkylselenophenes, benzo[6]selenophene and isomeric selenoloselenophenes (76CS(10)159). The commercial availability of thiophene makes comparable reactions of little interest for the obtention of the parent heterocycle in the laboratory. However, the reaction of substituted acetylenes with morpholinyl disulfide is of some synthetic value. The process, which appears to entail the initial formation of thionitroxyl radicals, converts phenylacetylene into a 3 1 mixture of 2,4- and 2,5-diphenylthiophene, methyl propiolate into dimethyl thiophene-2,5-dicarboxylate, and ethyl phenylpropiolate into diethyl 3,4-diphenylthiophene-2,5-dicarboxylate (Scheme 83a) (77TL3413). Dimethyl thiophene-2,4-dicarboxylate is obtained from methyl propiolate by treatment with dimethyl sulfoxide and thionyl chloride (Scheme 83b) (66CB1558). The rhodium carbonyl catalyzed carbonylation of alkynes in alcohols provides 5-alkoxy-2(5//)-furanones (Scheme 83c) (81CL993). The inclusion of ethylene provides 5-ethyl-2(5//)-furanones instead (82NKK242). The nickel acetate catalyzed addition of r-butyl isocyanide to alkynes provides access to 2-aminopyrroles (Scheme 83d) (70S593). 

A good solids-hquid separator performs well in service, both initially and over time. It operates rehably day after day, with enough flexibility to accommodate to normal fluctuations in process conditions, and does not require frequent maintenance and repair. Selection of such a separator begins with a preliminary hsting of a number of possible devices, which may solve the problem at hand, and usually ends with the purchase and instaUation of one or more commercially available machines of a specific type, size, and material of construc tion. Rarely is it worthwhile to develop a new land of separator to fill a particular need. 

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