Removal by acid treatment

Metal Treatment. After rolling, the oxide scale on sheet steel is removed by acid treatment (pickling) (see Metal surface treatments). Phosphoric acid, a good pickling agent, leaves the steel coated with a thin film of iron phosphates. This process improves mst resistance but presents a problem if the steel is to be electroplated. 

Preparation. Boron carbide is most commonly produced by the reduction of boric oxide with carbon in an electric furnace between 1400 and 2300°C. In the presence of carbon, magnesium reduces boric oxide to boron carbide at 1400—1800°C. The reaction is best carried out in a hydrogen atmosphere in a carbon tube furnace. By-product magnesium compounds are removed by acid treatment. 

After purification the DMT group from the oligonucleotide is removed by acid treatment, such as, acetic acid or some other milder acid in aqueous solution. After final detritylation, the salts if excessive are removed via precipitation, and then the product is lyophilized. Several process improvements have been tried and implemented to enable processing at the kilogram scale in our GMP facilities.1,47... 

Mitsunobu reaction as well as by mesylation and subsequent base treatment failed, the secondary alcohol was inverted by oxidation with pyridinium dichromate and successive reduction with sodium borohydride. The inverted alcohol 454 was protected as an acetate and the acetonide was removed by acid treatment to enable conformational flexibility. Persilylation of triol 455 was succeeded by acetate cleavage with guanidine. Alcohol 456 was deprotonated to assist lactonization. Mild and short treatment with aqueous hydrogen fluoride allowed selective cleavage of the secondary silyl ether. Dehydration of the alcohol 457 was achieved by Tshugaejf vesLCtion. The final steps toward corianin (21) were deprotection of the tertiary alcohols of 458 and epoxidation with peracid. This alternative corianin synthesis needed 34 steps in 0.13% overall yield. 

The cobalt-bound methyl group of (4) is not readily removed by acid. Treatment of (4) with acid in aqueous solution leads to proteolytic decoordination of the nucleotide base (pXa = 2.9). The cobalt-bound methyl group of methyl-Co "-corrins can be abstracted (1) by nucleophiles, such as thiol(ate)s, " > " (2) by radicaloid species, such as other Co"-corrins, or (3) by electrophilic species, such as Hg"-ions. A reversible and rapid methyl-group transfer occurs in deoxygenated aqueous solution between methyl-Co "-corrins and Co -corrins. From the pair, methyl-Co "-cobinamide and Co -cobalamin (6), methylcobalamin (4) and Co -cobinamide are generated and prevail at equilibrium. 

Hydrothermally dealuminated PER and sample that were subsequently acid treated exhibited better selectivities for isobutylene formation than an untreated PER catalyst (27). Furthermore, hydrothermally dealuminated PER exhibited a lower activity than untreated PER but higher selectivity for isobutylene 30,62,66). A subsequent acid treatment (with 5% HCl solution) further decreased the conversion and increased the isobutylene selectivity. The hydrothermal treatment created mesoporosity by A1 extraction. The A1 extraframework species were located in the mesopores and/or in the micropores. The HCl treatment removed part of the extraframework Al, leaving part in the micropores. The elimination of extraframework A1 from the mesopores was evidently beneficial for isobutylene selectivity. Evidently, the active sites associated with extraframework Al located in large voids are nonselective in contrast, extraframework Al located in the micropores (and not removed by acid treatment) does not contribute to catalytic activity. The steamed and acid-washed ferrierite exhibits excellent isobutylene selectivity and catalytic stability 30). 

Where necessary, the harmful nitrogen compounds can be removed by acid treatment (224,345) or the nitrogen can be selectively eliminated by hydrogenation (66). 

STEP 4 The BOC protecting group is removed by acid treatment. 

Ash removal by acid treatment before or after activation... 

Mineralization of the organic matter begins by transformation of the a-amino groups into ammonia. This conversion is observed in the acid-soluble fraction obtained when carbonates are removed by acid treatment of the sediment prior to alkaline extraction. In this fraction, the ratio of ammonium nitrogen to a-amino nitrogen increases steadily with burial in the first few meters of the sediment (Jocteur-Monrozier and Jeanson, 1981). However, these data are not always easy to interpret due to the dissolution, diffusion, and adsorption of ammonium nitrogen on clay minerals. 

F irther worl l with the t-amyloxycarbonyl group showed that it is comparable to the t-butyloxycarbonyl group. The furfuryloxycarbonyl group was foTind to be between the t-butyloxycarbonyl and benzyloxycarbonyl groups in ease of removal by acid treatment. 2... 

Carboxy groups may be protected by reaction with 2-amino-2-methylpropanol the resulting 4,4-dimethyl-4,5-dihydro-l,3-oxazol is inert to organomagnesium halide reagents and can be removed by acid treatment ... 

P) The hydrazone can now be hydrolyzed. The carbonyl group thus formed at Ce may now be reduced, and the bromine removed from Ci, both by treatment with LiAlHi, This reagent gives the correct stereochemistry in the reduction. The remaining methyl ether linkage is removed by acid treatment to give morphine. 

Selective phosphorylation. One advantage of this reagent is that the /-butyl groups are removable by acid treatment. It reacts readily only with primary alcohols, but does react with alkoxides of both primary and secondary alcohols (equation I). However, it reacts significantly faster with alkoxides of primary... 

The isopropylidene protecting groups of the sugar units were easily removed by acid treatment, leading to porphyrins 214a-216a. 

N-Glycosylnitrones have received considerable attention as chiral equivalents in enantioselective synthesis because the glycosyl moiety acts as an auxiliary, which can be easily removed by acid treatment at an advanced stage of a synthetic sequence. Concerning cycloadditions, it has mainly been AT-glycosylnitrones derived from formaldehyde (C-unsubstituted) [43-45], from glyoxylates (C-alkoxycarbonyl) [46-51], or from aromatic aldehydes (C-aryl) [52,53] that have been used, and these compounds usually showed very interesting stereoselectivities. 

In some preparation procedures, the surface of the silica can be covered with sodium or ammonium ions. They can be removed by treatment with an acid. Similarly, any surface contamination by other metal ions can be removed by acid treatment. 

It is well known that olefins may form complexes with some metals [80, 81]. Mercuric acetate can form complexes with polyolefins selectively, being removed by acid treatment [82]. Such complexes have been used in the separation of unsaturated fatty acids from mixtures [83]. Subbarao [84] has protected olefins aginst reduction using silver complexes, and Cope used reversible platinum complex formation [85, 86] for the resolution of medium ring trans olefins. Landesburg [87] used the iron tricarbonyl complex of the alcohol (13) to protect it during oxidation to the ketone (14) which was regenerated from the complex by photolysis [88a]. 

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