Formic Acid acidic solvent, 359 preparation

Cohen et al. [78] and Figueroa et al. [79] investigated the influence of the solvent composition and the rate of matrix crystallisation. Cohen s group concluded that high molecular mass peptides must be prepared with a solvent that includes formic acid (solvent pH<1.8) and a slow crystallisation. On the other hand, for low Mr peptides, better results are obtained with trifluoroacetic acid/acetonitrile solvent (solvent pH 2) and fast solvent evaporation. Figueroa s group also showed the importance of water concentration in the solvent. 

Bromo-4-methoxy-A-homo-estra-2,4,5(10)-trien-17-one (44 0. 2g), is dissolved in formic acid, 2 ml of boron trifluoride etherate is added and the mixture is stirred vigorously at 0° for 2 hr. A brown mass ca. 0.12 g) is obtained after evaporation of the solvents at reduced pressure. This material is diluted with water and extracted with chloroform. The chloroform extracts are washed successively with water and saturated salt solution, dried over anhydrous magnesium sulfate and evaporated at reduced pressure to give 95 mg of a product which is purified by filtration through a column of neutral alumina and crystallization of the residue after evaporation of the solvent from ethyl acetate-petroleum ether. The resulting A-homo-estra-l(10),2,4a-triene-4,17-dione (45), mp 143-146°, is identical to the tropone (45) prepared from monoadduct 17-ketone (43a). 

Chitin films can be manufactured from DMAc solutions or by other approaches, for example, blend films of beta-chitin (derived from squid pens) and poly(vinyl alcohol) (PVA) were prepared by a solution casting technique from corresponding solutions of beta-chitin and PVA in concentrated formic acid. Upon evaporation of the solvent, the film having 50/50 composition was found to be cloudy [224]. 

C18-0119. In a biochemistry laboratory, you are asked to prepare a buffer solution to be used as a solvent for isolation of an enzyme. On the shelf are the following solutions, all 1.00 M formic acid (Za = 1.8 X 10 ), acetic acid = 1.8 x 10 ), sodium formate (NaHC02), and sodium acetate (NaCH3 CO2). Describe how you would prepare 1.0 L of a pH = 4.80 buffer solution... 

TLC analysis of oligomers was performed on Silica gel 60 aluminium sheet (Merk) using buthanol and formic acid (1 1.5) as solvent [26]. The dye reagent was prepared by dissolving 9.5 mg of 1,3 dihydroxynaphtalin (Aldrich) in 5 mL of ethanol/H2S04 mixture (1 0.05, V/V). The migration front (Rf) of each spot was measured and expressed as Rm, were ... 

The parent hexathiaadamantane (185) is obtained preparatively when a solution of formic acid and hydrochloric acid in nitrobenzene is allowed to stand for several weeks in a hydrogen sulfide atmosphere the product which separated is almost insoluble in all common solvents and purification presents a problem. Only large volumes of dimethyl sulfoxide at reflux serve for recrystallization.224 The reaction of thioacetic acid with formic acid in the presence of zinc chloride gives tetramethyl-(186), monomethyl-, dimethyl-and trimethylhexathiaadamantane derivatives (187).225 Other variations include the reaction of thioacetic acid with a /i-diketone,226 and the use of boron trifluoride227 or aluminum chloride as a catalyst.228... 

Sample preparation requires only dissolution of the sample to a suitable concentration in a mixture of water and organic solvent, commonly methanol, isopropanol, or acetonitrile. A trace of formic acid or acetic acid is often added to aid protonation of the analyte molecules in the positive ionization mode. In negative ionization mode ammonia solution or a volatile amine is added to aid deprotonation of the analyte molecules. 

The optimum conditions for the MS detection of anthocyanin derivatives have also been intensively studied. Grape skin extract was prepared by macerating skins with methanol-formic acid (95 5) for three days changing the extracting agent each day. The combined extracts were evaporated and diluted with water. RP-HPLC measurements were carried out in an ODS column (150 X 4.6 mm i.d. particle size 5 /an) at 30°C. The solvents were water-formic acid (90 10, v/v, A) and methanol-water-formic acid (45 45 10, v/v, B). The gradient was from 35 to 95 per cent B in 20 min to 100 per cent B in 5 min final hold... 

If UV transparency is an issue for sensitive detection, nonvolatile solvents have been used. These include phosphoric acid,152,53 and TEAP, 24 among others. The latter is preferred as it allows for pH adjustment (2.0-8) and is biocompatible in most in vitro biological systems. It has been proposed that the role of the added triethylamine (to phosphoric acid, formic acid, TFA, and acetic acid) is to cap the unreacted silanols present on the silica gel. This issue has been recently addressed in a short review. 54 The TEAP buffer has been used extensively for the isolation of natural products122 and synthetic peptides. 26 Preparatively, the TEAP buffers were found to be good first solvents to use as they are highly resolutive with a selectivity that is often different from that conferred by 0.1% TFA. Since excess TFA will be eliminated by lyophilization, it is used as the last purification and desalting step. 

Palladium complexes exhibit even higher catalytic activity and produce branched acids preferentially.132 133 The selectivity, however, can be shifted to the formation of linear acids by increasing the phosphine concentration.134 Temperature, catalyst concentration, and solvent may also affect the isomer ratio.135 Marked increase in selectivity was achieved by the addition of Group IVB metal halides to palladium136 and platinum complexes.137 Linear acids may be prepared with selectivities up to 99% in this way. The formic acid-Pd(OAc)2-l,4-bis(diphe-nylphosphino)butane system has been found to exhibit similar regioselectivities.138 Significant enhancements of catalytic activity of palladium complexes in car-bomethoxylation by use of perfluoroalkanesulfonic acid resin cocatalysts was reported.139,140... 

The best result so far available through a non-EG-acid approach has been obtained with 100% formic acid leading to the desired 69 in 32% yield after alkaline hydrolysis. In contrast, the electrolysis of 67 in an acetone—LiC104—(Pt) system at constant current (3.3 mA/cm2 for 1 h, 0.36 F/mol) in an undivided cell affords the desired alcohol 69 in 52 % yield together with 68 (25 %) (Scheme 3-25). The effect of the solvent is remarkable. Acetone is suitable for the selective preparation of 69, presumably because it traps the cationic intermediate, leading to an oxocarbenium ion, which... 

Aldonic and ketoaldonic acids may be difficult to separate. Norris and Campbell separated ketogluconic acid from gluconic acid by preparing the phenylhydrazone of the keto acid, which is then easily separable from gluconic acid. A methanol-ethanol-water solvent mixture was used.64 Another useful solvent developer is 1-butanol-formic acid-water.133 Macek and Tadra separated a series of ketoaldonic acids in a number of acidic solvent developers.134 Color reagents which may be used include ammoniacal silver nitrate,94 o-phenylenediamine dihydrochloride,84 and aniline acid oxalate.138 Lactones are detectable with hydroxylamine followed by ferric chloride.128... 

John et al. added twice the volume of ACN to plasma samples thus generating a supernatant containing 66 % (v/v) ACN. Merely dilution with aqueous HPLC solvent A [0.1 % formic acid (FA)] was necessary prior to injection allowing quantitative analysis of R- and. S -hyoscyaminc [49] as well as atropine, cocaine, homatropine, ipratropium, littorine, iV-buty 1-scopolamine and scopolamine, simultaneously [50], Recoveries were greater than 85 % (Table 2). Despite this crude preparation procedure effects on ionization were negligible. 

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