Protection from Moisture—Hydrolysis

Protection from Moisture.—The moisture in the air may act upon chemical preparations in a variety of ways. (1) It may combine with the preparation to form an entirely different compound, as when calcium oxide is converted into the hydroxide. (2) With very soluble salts it may occasion deliquescence (see Exercise 7). (3) It may occasion hydrolysis. This last case 

Hydrolysis.—A salt that contains as one of its constituents either a weak acid or a weak base will not dissolve in water to form a neutral solution. Water acts upon such a salt partially to reverse the reaction of neutralization, liberating equivalent parts of both acid and base. To obtain in solid form a normal salt that is subject to hydrolysis, it is necessary to have present in the solution considerable excess of either the acid or the base, depending upon the nature of the salt and the mother liquor from which the salt is crystallized will contain this excess. When the crystals have been drained from this mother liquor, they cannot be washed with the pure solvent, for this would leave them coated with a film of the aqueous solution of the normal salt, which would then undergo hydrolysis. If either the acid or the base of which the salt is composed should be difficultly soluble, 

References Friend, I, 227 Mellor, I, 1009 textbooks on physical chemistry. 

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Succinic acid and succinic anhydride are sold in 25-kg net polyethylene (PE) bags having cardboard box protection for the anhydride, in 70-liter (50-kg net) fiber dmms, and in 55-gaHon (275-lb 125-kg net) dmms. The two products must be stored in a fresh, dry, ventilated area. Succinic anhydride must be carefully protected from moisture during transportation and storage to avoid hydrolysis to succinic acid. 

Switzerland, and prepared according to a literature procedure, were used by the submitters without any noticeable difference. Lead tetraacetate was dried prior to use for at least 12 hours over potassium hydroxide and phosphorus pentoxide in an evacuated desiccator (12 mm.) that was protected from direct light. If well protected from moisture, lead tetraacetate can be kept for weeks in this way. However, after exposure to moisture in the air, lead tetraacetate usually turns brown from hydrolysis to lead hydroxide. The reactivity of such lead tetraacetate is diminished somewhat, but it can still be used. If the lead tetraacetate has turned black, the reagent should be recrystallized from glacial acetic acid and dried prior to use as described above. 

Potassium fluorosulfite is a colorless crystalline powder which, because of hydrolysis, smells of sulfur dioxide and which must necessarily be stored under protection from moisture. The following relationship applies for the sulfur dioxide vapor pressure over potassium fluorosulfite ... 

Ketene aminals must be protected from moisture. Rater causes a rapid hydrolysis of the ketene aminal giving a substituted acetamide and a mole of seoonday amine. 

This reaction, like all Neber rearrangements, is limited by availability of the appropriate oxime tosylate. Substrates in which the aryl group contain an electron-donating function are unstable, since they have a propensity to undergo Beckmann rearrangement. However, this difficulty can be resolved by subsequent conversion of the a-amino acetals. For example, catalytic hydrogenation of 2,2-diethoxy-2-(p-bromophenyl)ethylaraine yields the known parent compound, 2,2-diethoxy-2-phenylethylamine These two a-amino acetals readily undergo hydrolysis and should be protected from moisture. 

Features Its prods, offer resist, to hydrolysis, solvs., oil and microbes, low temp, behavior, and transparency Properties APHA < 50 max. liq. sol. in most org. solvs. barely sol. in water m.w. 2000 120 sp.gr. 1.048 (60 C) soften, pt. 18C acid no. < 0.05 hyd. no. 52.9-59.7 flash pt. 204 C < 0.03% water Storage Hygroscopic protect from moisture and air dry nitrogen blanket should be applied to open containers before resealing PolyTHF 250 [BASF BASF AG]... 

Partially hydrolyzed PVA is typically used in food industry. PVA is an odorless and tasteless, translucent, white or cream-colored granular powder. It is used as a moisture barrier film for food supplement tablets and for foods that contain inclusions or dry food with inclusions that need to be protected from moisture uptake. PVA is not known to occur as a natural product because it forms from hydrolysis. It is soluble in water and slightly soluble in ethanol, but it is insoluble in other organic solvents. A 5% solution of PVA typically exhibits a pH in the range of 5.0-6.5. PVA has a melting point of 180-190°C. It has a molecular weight of between 26,300 and 30,000 and a degree of hydrolysis of 86.5-89%. 

NOTE. The maleic anhydride should be finely ground and protected from moisture to prevent hydrolysis to the corresponding acid. A mixture of xylenes in the boiling-point range 137-140 °C will suffice. Use freshly distilled solvent or dry it over molecular sieves before use. Dispense the xylene in the hood using an automatic delivery pipet. In large laboratory sections it is recommended that the evolved SO2 be trapped (see Prior Reading). 

Dry chlorine has a great affinity for absorbing moisture, and wet chlorine is extremely corrosive, attacking most common materials except HasteUoy C, titanium, and tantalum. These metals are protected from attack by the acids formed by chlorine hydrolysis because of surface oxide films on the metal. Tantalum is the preferred constmction material for service with wet and dry chlorine. Wet chlorine gas is handled under pressure using fiberglass-reinforced plastics. Rubber-lined steel is suitable for wet chlorine gas handling up to 100°C. At low pressures and low temperatures PVC, chlorinated PVC, and reinforced polyester resins are also used. Polytetrafluoroethylene (PTFE), poly(vinyhdene fluoride) (PVDE), and... 

Aluminum chloride and its derivatives are the most familiar Lewis acids and are routinely employed in many Lewis acid-promoted synthetic transformations. The first polymer-supported metal Lewis acids to be studied were polymers attached by weak chemical or physical interactions to a Lewis acid. In the 1970s Neckers and coworkers reported the use of styrene-divinylbenzene copolymer-supported AlCl,- or BF3 as catalyst in condensations, esterifications, and acetalization of alcohols [11,12]. This type of polymer-supported AICI3 (1) is readily prepared by impregnation of a polystyrene resin with AICI3 in a suitable solvent. Subsequent removal of the solvent leaves a tightly bound complex of the resin and AICI3. The hydrophobic nature of polystyrene protects the moisture-sensitive Lewis acid from hydrolysis, and in this form the Lewis acid is considerably less sensitive to deactivation by hydrolysis. This polymer complex could be used as a mild Lewis acid catalyst for condensation of relatively acid-sensitive dicyclopropylcarbinol to an ether (Eq. 1) [13],... 

Add halides are important intermediates and they are used extensively for the conversion of carboxylic adds into other derivatives. For example, add halides can be used to prepare (in addition to amides) anhydrides, esters, aldehydes, and ketones. Add halides readily undergo reaction with water (hydrolysis) to form the corresponding carboxylic add. For this reason the reaction system must be protected from atmospheric moisture when add halides are formed and/or used. 

Trityl-based resins are highly acid-labile. The steric hindrance of the linker prevents diketopiperazine formation and the resins are recommended for Pro and Gly C-terminal peptides. Extremely mild acidolysis conditions enable the cleavage of protected peptide segments from the resin. These resins are commercially available as their chloride or alcohol precursors. The trityl chloride resin is extremely moisture-sensitive, so reagents and glassware should be carefully dried before use to avoid hydrolysis into the alcohol form. It is necessary to activate the trityl alcohol precursor and it is highly recommended to reactivate the chloride just before use see Note 4). After activation, attachment of the first residue occurs by reaction with the Fmoc amino acid derivative in the presence of a base. This reaction does not involve an activated species, so it is free from epimerization. Special precautions should be taken for Cys and His residues that are particularly sensitive to epimerization during activation (Table 2). 

Disproportionation of the sulfonates yields triarylbismuthine and arylbismuth disulfonate. Several diarylbismuth triflate-HMPA complexes are prepared by the action of trimethylsilyl triflate and methanol on triarylbismuthines in the presence of HMPA [960M1951]. These complexes are stable colorless crystals or oils, readily soluble in CH2CI2, CHCI3, benzene, THF and methanol without decomposition. The HMPA ligand is effective in protecting the triflates from hydrolysis by atmospheric moisture without HMPA, these triflates become less stable in open air. H-... 

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