Mercaptans salts

Racemic 1 could be obtained in excellent yield by the cycloaddition with vinyl acetic acid, but we did not discover any efficient means to convert this directly into 10b that didn t involve mercaptan salts. The thioester could be produced directly by reaction with the propyl thioester of vinyl acetic acid, however its preparation similarly demanded copper mercaptan. Our previous work had created an excellent process for preparing 9. This chemistry had by now been demonstrated numerous times in our pilot plant. It was a well-established large-scale process and we could avoid repeating scale-up work related to reagent sourcing, thermochemistry, engineering, and analytical if we could efficiently transesterify this directly to 10 b. This became our primary goal. 

Tripeptide Ser-His-Asp had been introduced to the CD for simulating the chymotrypsin by the following method. Mix 2-amino ethyl mercaptan salts, 6-0-tosyl-/3-CD and NH4HCO3 with DMF/H2O (1 3) solution under nitrogen protection at 60 C for 4h. After vacuum concentration, separate the product by Sephadex G-10 column. The yield is about 43%. Mix the above product with Boc-Ser (Ot-Bu) -His-Asp (Ot-Bu) OH, dicyclohexyl carbodiimide, 1-hydroxy triazole in DMF solution to obtain 6-[Boc-Ser (Ot-Bu) -His-Asp (Ot-Bu) NHCH2CH2S]-/3-CD. Then treat with the TFA/CH2C12(9 1) mixed solution, vacuum concentrate and freeze-dry. This modified CD can be used as an analogue enzyme to hydrolyze nitrophenol esters. 

Dissolve (or suspend) 0-25 g. of the acid in 5 ml. of warm water, add a drop or two of phenolphthalein indicator and neutralise carefully with ca. N sodium hydroxide solution. Then add 2-3 drops of ca. O lN hydrochloric acid to ensure that the solution is almost neutral (pale pink colour). (Under alkaline conditions the reagent tends to decompose to produce the evil-smelling benzyl mercaptan.) If the sodium salt is available, dissolve 0-25 g. in 5 ml. of water, and add 2 drops of ca. 0 -hydrochloric acid. Introduce a solution of 1 g. of S-benzyl-iso-thiuro-nium chloride in 5 ml. of water, and cool in ice until precipitation is Dibasic and tribasic acids will require 0-01 and 0-015 mol respectively. 

Alkyl mercaptans are partly soluble in solutions of caustic alkalis, but their salts are hydrolysed in dilute aqueous solution back to the free mercaptans. Thiophenols are soluble in alkah hydroxide solutions. Upon treatment with sodium, hydrogen is evolved. 

Hypochlorites, salts of Urea, amines, anthracene, carbon, carbon tetrachloride, ethanol, glycerol, mercaptans, organic sulfides, sulfur, thiols... 

Nitroethane. The principal use of nitroethane is as a raw material for synthesis in two appHcations. It is used to manufacture a-methyl dopa, a hypertensive agent. Also, the insecticide 3 -methyl-A/-[(methylcarbamoyl)oxy]thioacetimidate [16752-77-5] can be produced by a synthesis route using nitroethane as a raw material. The first step of this process involves the reaction of the potassium salt of nitroethane, methyl mercaptan, and methanol to form methyl methylacetohydroxamate. Solvent use of nitroethane is limited but significant. Generally, it is used in a blend with 1-nitropropane. 

Hydrogen Sulfide andMercaptans. Hydrogen sulfide and propylene oxide react to produce l-mercapto-2-propanol and bis(2-hydroxypropyl) sulfide (69,70). Reaction of the epoxide with mercaptans yields 1-aLkylthio- or l-arylthio-2-propanol when basic catalysis is used (71). Acid catalysts produce a mixture of primary and secondary hydroxy products, but ia low yield (72). Suitable catalysts iaclude sodium hydroxide, sodium salts of the mercaptan, tetraaLkylammonium hydroxide, acidic 2eohtes, and sodium salts of an alkoxylated alcohol or mercaptan (26,69,70,73,74). 

Whereas other metal salts, especially lead stearates and srdfates, or mixtures of Groups 2 and 12 carboxylates (Ba—Cd, Ba—Zn, Ca—Zn) ate also used to stabilize PVC, the tin mercaptides are some of the most efficient materials. This increased efficiency is largely owing to the mercaptans. The principal mechanism of stabilization of PVC, in which all types of stabilizers participate, is the adsorption of HCl, which is released by the PVC during degradation. This is important because the acid is a catalyst for the degradation, thus, without neutralization the process is autocatalytic. 

Alternatively, the metathesis can be effected by sulfites or bisulfites that convert cystine iato one cysteiae residue and one thiosulfate (Bunte salt) residue. Hair waving based on sulfites is slower than that based on mercaptans and is more likely to cause changes ia hair color. 

Dissociation extraction is the process of using chemical reac tion to force a solute to transfer from one liquid phase to another. One example is the use of a sodium hydroxide solution to extract phenolics, acids, or mercaptans from a hydrocarbon stream. The opposite transfer can be forced by adding an acid to a sodium phenate stream to spring the phenolic back to a free phenol that can be extrac ted into an organic solvent. Similarly, primary, secondary, and tertiary amines can be protonated with a strong acid to transfer the amine into a water solution, for example, as an amine hydrochloride salt. Conversely, a strong base can be added to convert the amine salt back to free base, which can be extracted into a solvent. This procedure is quite common in pharmaceutical production. 

The lead acetate removes any unreacted m ethyl mercaptan by precipitating it as the lead salt. 

Purified via the mercury salt [see Kern J Am Chem Soc 75 1865 1953], which was crystd from benzene as needles (m 121°), and then dissolved in CHCI3. Passage of H2S gas regenerated the mercaptan. The HgS ppte was filtered off, and washed thoroughly with CHCI3. The filtrate and washings were evaporated to remove CHCI3, then residue was fractionally distd under reduced pressure [Mackle and McClean, Trans Faraday Soc 58 895 1962]. 

Dissolved in EtOH, and added to 0.25M Pb(OAc)2 in 50% aqueous EtOH. The ppted lead mercaptide was filtered off, washed with a little EtOH, and impurities were removed from the molten salt by steam distn. After cooling, dilute HCl was added dropwise to the residue, and the mercaptan was distd directly from the flask. Water was separated from the distillate, and the mercaptan was dried (Na2C03) and distd under nitrogen. [Mathias J Am Chem Soc 72 1897 1950.]... 

Other direct methods for the sulfonation of the higher fatty acids are by the use of sulfur trioxide vapor or by the use of chlorosulfonic acid. Indirect methods are also available for the preparation of a-sulfo fatty acids and their salts from an a-bromo fatty acid made by the Hell-Volhard-Zelinsky reaction. The bromo compound may be converted directly to the sodium salt of a sulfonic acid through the Strecker reaction or may be converted to the mercaptan and oxidized to the sulfonate. Sulfonation of the lower fatty acids has been studied by Backer and co-workers. ... 

Washing light hydrocarbons with water is a common refinery practice. It finds application on the feed to catalytic polymerization plants. It is used to remove any entrained caustic from the mercaptan removal facilities as well as any other impurities such as amines which tend to poison the polymerization catalyst. Another use for water wash is in alkylation plants to remove salts from streams, where heating would tend to deposit them out and plug up heat exchanger surfaces. Water washing can be carried out in a mixer- settler, or in a tower if more intimate contacting is necessary. 

---