Buffers acetate

A second synthesis of cobyric acid (14) involves photochemical ring closure of an A—D secocorrinoid. Thus, the Diels-Alder reaction between butadiene and /n j -3-methyl-4-oxopentenoic acid was used as starting point for all four ring A—D synthons (15—18). These were combined in the order B + C — BC + D — BCD + A — ABCD. The resultant cadmium complex (19) was photocyclized in buffered acetic acid to give the metal-free corrinoid (20). A number of steps were involved in converting this material to cobyric acid (14). 

Tribromophenol can be further brominated in buffered acetic acid to give 2,4,4,6-tetrabromo-2,5-cyclohexadien-l-one [20244-61-5] a useful hrominating agent (26). 

The bromination of 4,5-j -dihydrocortisone acetate in buffered acetic acid does not proceed very cleanly (<70%) and, in an attempt to improve this step in the cortisone synthesis, Holysz ° investigated the use of dimethylformamide (DMF) as a solvent for bromination. Improved yields were obtained (although in retrospect the homogeneity and structural assignments of some products seem questionable.) It was also observed that the combination of certain metal halides, particularly lithium chloride and bromide in hot DMF was specially effective in dehydrobromination of 4-bromodihydrocortisone acetate. Other amide solvents such as dimethylacetamide (DMA) and A-formylpiperidine can be used in place of DMF. It became apparent later that this method of dehydrobromination is also prone to produce isomeric unsaturated ketones. When applied to 2,4-dibromo-3-ketones, a substantial amount of the A -isomer is formed. 

The dehydrogenation of 2,3-dihydro- and 2,5-dihydro-l//-l-benzazepines to 3//-l-benz-azepincs with heterocyclic enamines in the presence of boron trifluoride diethyl ether complex has been achieved in moderate yields (30-35%).241 In contrast, electrochemical oxidation of 2,5-dihydro-1 H- -benzazepines in buffered acetic acid solution furnishes initially 5//-l-benz-azepines in 35-45% yield.242... 

With a given weak acid, a buffer soiution can be prepared at any pH within about one unit of its p vaiue. Suppose, for exampie, that a biochemist needs a buffer system to maintain the pH of a soiution ciose to 5.0. What reagents shouid be used According to the previous anaiysis, the weak acid can have a p Z a between 4.0 and 6.0. As the p deviates from the desired pH, however, the soiution has a reduced buffer capacity. Thus, a buffer has maximum capacity when its acid has its p as ciose as possibie to the target pH. Tabie 18-1 iists some acid-base pairs often used as buffer soiutions. For a pH - 5.0 buffer, acetic acid (p Za — 4.75) and its conjugate base, acetate, wouid be a good choice. 

Levy G, Hayes BA. Physicochemical basis of the buffered acet-ylsalicylic acid controversy. N Engl J Med 1960 262(21) 1053-1058. 

Adding an acid to a buffer Acetate ions react with the hydronium ions added to the solution. 

Treatment of a series of metal acetylacetonates with the N-halogen suc-cinimides in boiling chloroform afforded the trihalogenated metal chelates in high yields. The use of bromine or iodine monochloride in buffered acetic acid also yielded the bromo- and iodochelates (7). 

Other groups have also studied the transmethylation of mercuric acetate their values agree reasonably well with those of DeSimone et al.. and are listed in Table I (34-37). One group found no formation of 2 in the Hg(OAc)2-l reaction in buffered acetic acid (36). 

One early paper reported that Tl(III) reacted with 1 to give an uncharacterized methylthallium(III) product (31). A second-order reaction occurs between Tl(OAc)i" and 1 in buffered acetic acid, with a rate constant of 72.5 M- sec-1 (46a) an earlier reported value of 1.60M 1 sec-1 is too low (47). As in the analogous Hg(II) systems (46a. 51), halide ions retard transmethylation of Tl(III). Thallous ion reacts only very slowly with 1 to give (CH3)2T1+ (46). 

Figure 9 HPLC chromatograms (UY detection, 205 nm) obtained on solutions of LY334370 hydrochloride in (4) water exposed to simulated sunlight for 20 hr, (5) water/acetonitrile containing the radical initiator AIBN held at 40°C for 8 days, (6) 0.3% hydrogen peroxide held in the dark at 23°C for 8 days, (7) pH 8 buffer/acet-onitrile held at 70°C for 8 days.

Will precipitate Ni(ll) in the presence of NH3 or buffered acetate Pd(ll) in HCI solution the addition of tartaric acid to the reagent will mask Fe(lll) and Cr(lll) interferences Pd(ll) and Bi(lll) will also precipitate... 

The analyte content was 5-10 ppm, with a ligand concentration in excess (ca. ten times with respect to the metal ion). The pH was adjusted with a proper buffer (acetic acid / acetate or chloroacetic acid / chloroacetate) and inert salt (NaNO ) was added in order to increase the density of the aqueous rich lower phase, which facilitates fast centrifugation. 

Buffer-Acetic acid (50 ml)-water (930 ml) pH 3.4 with 1 N sodium hydroxide C-18 Buffer-acetonitrile... 

The scope of the 2-azadiene intramolecular Diels-Alder cyclization, employed for the synthesis of the daphniphyllum alkaloids, has been further investigated by Heathcock et al.[76j. The protocol involves Moffatt-Swem oxidation of the 1,5-diol to the dialdehyde, and treatment of the crude methylene chloride solution with ammonia followed by solvent exchange from methylene chloride to a buffered acetic add solution. The cydopentyl ring, quaternary carbon and tertiary carbon centers in... 

Amikacyna, cefazolin, deksametazon, desmetylosildenafil, dipyron, flukonazol, furosemid, imipenem, ketoprofen, paracetamol, prednizolon, sildenafil wankomycyna/ urine HPLC DAD Column LiChroCART Purospher STAR, RP-18e, (125 X 3 mm, 5 pm) Mobile phase ACN buffer (acetic acid, sodium acetate, pH 4.66) 0.05 % TFA in water (gradient elution) Detection DAD 2 = 200-450 nm Extraction LLE/acetate dichloromethane chloroform (45 35 20 v/v/v) LOD 0.01-1.16 pg/mL LOQ 0.02-3.45 pg/mL [74]... 

Oxidative cycllzatiou of dienes. Dienes are oxidized with formation of a new carbon-carbon bond by catalytic amounts of PdCl2 and CuClj [to regenerate Pd(II)] in NaOAc-buffered acetic acid. ... 

Acetate and other carboxylate-based buffers Acetate can be used in the range 4.0-5.5 and, as a naturally occurring substance, it is compatible with nearly all reactions. For lower pH values (pH 3.0-4.5) formate can be used. Succinate, and also, importantly, citrate have the advantage of buffering over a broad pH range (succinate pH 3.5-6.5, citrate pH 2.5—7.0) since they contain respectively two and three carboxylate groups. However, they act as chelators for several metal ions (e.g., Ca2+, Mg2, Zn2+, and Fe3+) which makes them unsuitable for many applications. 

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