Mercaptoethanols

The most commonly used protected derivatives of aldehydes and ketones are 1,3-dioxolanes and 1,3-oxathiolanes. They are obtained from the carbonyl compounds and 1,2-ethanediol or 2-mercaptoethanol, respectively, in aprotic solvents and in the presence of catalysts, e.g. BF, (L.F. Fieser, 1954 G.E. Wilson, Jr., 1968), and water scavengers, e.g. orthoesters (P. Doyle. 1965). Acid-catalyzed exchange dioxolanation with dioxolanes of low boiling ketones, e.g. acetone, which are distilled during the reaction, can also be applied (H. J. Dauben, Jr., 1954). Selective monoketalization of diketones is often used with good success (C. Mercier, 1973). Even from diketones with two keto groups of very similar reactivity monoketals may be obtained by repeated acid-catalyzed equilibration (W.S. Johnson, 1962 A.G. Hortmann, 1969). Most aldehydes are easily converted into acetals. The ketalization of ketones is more difficult for sterical reasons and often requires long reaction times at elevated temperatures. a, -Unsaturated ketones react more slowly than saturated ketones. 2-Mercaptoethanol is more reactive than 1,2-ethanediol (J. Romo, 1951 C. Djerassi, 1952 G.E. Wilson, Jr., 1968). 

An important aspect of this is the splitting of the polymer chain with thiol (eq. 5) or mercaptide ion (thiol + base catalyst). In fact, sodium sulfide or organic monothiols, eg, mercaptoethanol or decyhnercaptan, are utilized to lower the molecular weight of polysulftdes or to limit the extent of curing reactions. 

For deterrnination of tryptophan, 4 M methanesulfonic acid hydrolysis is employed (18). For cystine, the protein is reduced with 2-mercaptoethanol, the resultant cysteine residue is carboxymethylated with iodoacetic acid, and then the protein sample is hydroly2ed. Also, a one-pot method with mercaptoethanesulfonic acid has been developed for tryptophan and cystine (19). 

The most widely appHed colorimetric assay for amino acids rehes upon ninhydrin-mediated color formation (129). Fluorescamine [38183-12-9] and (9-phthalaldehyde [643-79-8] are popular as fluorescence reagents. The latter reagent, ia conjunction with 2-mercaptoethanol, is most often used ia post-column detection of amino acids separated by conventional automated amino acid analysis. More recently, determiaation by capillary 2one electrophoresis has been developed and it is possible to determine attomole quantities of amino acids (130). 

Thiols must be added before or within a very short time after irradiation to protect against ceU killing. This is apparent from conventional cell survival data (9) but is even better illustrated by kinetic studies showing that 2-mercaptoethanol (see Table 1) protects oxic V79 cells when added just before but not 7 milliseconds after irradiation (5). 

A fermented-egg product (EEP), patented as an attractive bait for synanthropic flies, has been shown to be attractive to coyotes and repeUent to deer (79). Its components are variable, with relative concentrations of 77% fatty acids, 13% bases, and 10% (primarily) neutrals composed of at least 54 volatiles such as ethyl esters, dimethyl disulfide, and 2-mercaptoethanol. Synthetic formulations have been evaluated to find a replacement for a patented fermented-egg protein product that attracts coyotes and repels deer. Ten aUphatic acids (C-2 to C-8), four amines (pentyl, hexyl, heptyl, and trimethyl), dimethyl disulfide, 2-mercaptoethanol, and 54 more volatiles (C-1 to C-5 esters of C-1 to C-8 acids) have been tested as synthetic fermented egg (SEE) (80) in approximately the same proportions that are present in EEP. Weathering was a problem that caused decreased efficacy, which suggests trials of controUed-release formulations. Eourteen repeUents have been examined against white-taU deer in Peimsylvania in choice tests when treated onto sheUed com (81). 

Fig. 3. Sodium dodecyl sulfate—polyacrylamide gel electrophoretic pattern for molecular weight standards (lane 1) water-extractable proteins of defatted soybean meal (lane 2) purified IIS (glycinin) (lane 3) and purified 7S (P-conglycinin) (lane 4) where the numbers represent mol wt x 10. The gel was mn in the presence of 2-mercaptoethanol, resulting in the cleavage of the disulfide bond linking the acidic (A bands) and basic (B bands) polypeptides of the...

Arachin, the counterpart of glycinin in peanuts, consists of subunits of 60,000—70,000 mol wt which on reduction with 2-mercaptoethanol yield polypeptides of 41,000—48,000 and 21,000 mol wt (17) analogous to the behavior of glycinin. In addition to the storage proteins, oilseeds contain a variety of minor proteins, including trypsin inhibitors, hemagglutinins, and enzymes. Examples of the last are urease and Hpoxygenase in soybeans. 

It also reacts with epoxides forming 2-hydroxyalkyl thiols, eg, 2-mercaptoethanol [60-24-2] and bis(2-hydroxyalkyl) sulfides such as bis (2-hydroxyethyl) sulfide [111-48-8], both products are made commercially ... 

The oxirane ring-opening reaction requires the presence of a basic catalyst. An acidic catalyst also works, but the polymerization of the oxirane limits its usehilness. In the case of 2-mercaptoethanol (eq. 8), the product has been found to be autocatalytic, ie, the product is a catalyst for the reaction. 

The by-products of these reactions are sulfides. The sulfide formed in the synthesis of 2-mercaptoethanol, 3-thia-l,5-pentanediol (thiodiglycol), has a variety of uses ranging from lubricant additive intermediates to textile finishing. 

This type of chemistry also functions for hydroxyketones and aldehydes. The process using 1,2-ethanedithiol or 2-mercaptoethanol results in cycHc stmctures (eq. 25). The 1,3-ditholenes (X = S) and 1,3-thioxalanes (X = O) resulting from these reactions have been shown to be of interest commercially. 

Thiols iateract readily with many mbber-containing materials. For this reason, care should be taken ia the selection of gasket and hose materials. Teflon, Kel-F, Viton, or other suitable fluoroelastomers function as gasket materials. Viton is suitable for hoses. Carbon steel is useful for many thiols, although some thiols become very discolored when carbon steel is utilized. In these cases, the use of stainless steel is very desirable. Isolation from air and water also minimizes color formation. 2-Mercaptoethanol and 1,2-ethanedithiol should be stored ia stainless steel (61). 

Various techniques have been studied to increase sohds content. Hydroxy-functional chain-transfer agents, such as 2-mercaptoethanol [60-24-2], C2HgOS, reduce the probabihty of nonfunctional or monofunctional molecules, permitting lower molecular-weight and functional monomer ratios (44). Making low viscosity acryhc resins by free-radical initiated polymerization requires the narrowest possible molecular-weight distribution. This requires carehil control of temperature, initiator concentration, and monomer concentrations during polymerization. 

Cyclohexane-1,2-dione reacts with ethylene glycol (TsOH, benzene, 6 h) to form the diprotected compound. Monoprotected 1,3-oxathiolanes and 1,3-dithiolanes are isolated on reaction under similar conditions with 2-mercaptoethanol and eth-anedithiol, respectively. ... 

The Npys group can be. cleaved reductively with BU3P, H2O or mercaptoethanol. It is stable to CF3COOH (24 h), 4 M HCl/dioxane (24 h), and HF (1 h). The related reagent, 2-pyridinesulfenyl chloride, has also been proposed as a useful reagent for the deprotection of the 5-trityl, 5-diphenylmethyl, 5-acetamidomethyl, 5-/-butyl, and S-r-butylsulfenyl groups, but this reagent is very susceptible to hydrolysis. ... 

The dinitrophenyl group has been used to protect the imidazole — NH group in histidines (45% yield)" by reaction with 2,4-dinitrofluorobenzene and potassium carbonate. Imidazole —NH groups, but not a-amino acid groups, are quantitatively regenerated by reaction with 2-mercaptoethanol (22°, pH 8, 1 h)." The 2,4-... 

Mercaptoethanol Mesityl oxide a-Methacrylic acid Methane... 

Dipping solution Make 0.1 g o-phthalaldehyde (phthaldialdehyde, OPA) and 0.1 ml 2-mercaptoethanol (2-hydroxy-l-ethanethiol) up to 100 ml with acetone. 

In the presence of 2-mercaptoethanol o-phthalaldehyde reacts with primary amines to yield fluorescent isoindole derivatives [20] ... 

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