Alkaline conditions

Stannate(II) ions are powerful reducing agents. Since, for tin, the stability of oxidation state -b4 is greater than that of oxidation state -b2, tin(II) always has reducing properties, but these are greater in alkaline conditions than in acid (an example of the effect of pH on the redox potential, p. 101). 

This is only found in the green manganatef VI) ion. already described. It is only stable in alkaline conditions in neutral or acid solution it disproportionates ... 

Cobaltilll) oxide is obtained as a brown precipitate Co Oj.aq when cobalt(II) hydroxide is oxidised in alkaline conditions (or when a cobalt(III) is decomposed by aqueous alkali). On heating it gives the black mixed oxide C03O4. 

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. 

A special application of the Japp-Klingemann/Eischer sequence is in the preparation of tryptamines from piperidone-3-carboxylate salts, a method which was originally developed by Abramovitch and Shapiro[2]. When the piperidone is subjected to Japp-Klingemann coupling under mildly alkaline conditions decarboxylation occurs and a 3-hydrazonopiperidin-2-one is isolated. Fischer cyclization then gives 1-oxotetrahydro-p-carbolines which can be hydrolysed and decarboxylated to afford the desired tryptamine. 

Indoles can also be alkylated by conjugate addition under alkaline conditions. Under acidic conditions, alkylation normally occurs at C3 (see Section 11.1). Table 9.1 includes examples of alkylation by ethyl acrylate, acrylonitrile, acrylamide and 4-vinylpyridine. 

The alkaline conditions of the reduction with aqueous sodium borohydride leads to competitive reactions of the OH nucleophile, but the product usually obtained from a thiazolium salt (195) is the corresponding thiazolidine (196). 

Active Raney nickel induces desulfurization of many sulfur-containing heterocycles thiazoles are fairly labile toward this ring cleavage agent. The reaction occurs apparently by two competing mechanisms (481) in the first, favored by alkaline conditions, ring fission occurs before desul-, furization, whereas in the second, favored by the use of neutral catalyst, the initial desulfurization is followed by fission of a C-N bond and formation of carbonyl derivatives by hydrolysis (Scheme 95). 

One standard method for determining the dissolved O2 content of natural waters and wastewaters is the Winkler method. A sample of water is collected in a fashion that prevents its exposure to the atmosphere (which might change the level of dissolved O2). The sample is then treated with a solution of MnS04, and then with a solution of NaOH and KI. Under these alkaline conditions Mn + is oxidized to Mn02 by the dissolved oxygen. 

Hydrolysis in neutral aqueous solutions proceeds slowly at room temperature and more rapidly at acidic conditions and elevated temperatures. The hydrolysis—esterification reaction is reversible. Under alkaline conditions hydrolysis is rapid and irreversible. Heating the alkaline hydrolysis product at 200—250°C gives 4,4 -oxydibutyric acid [7423-25-8] after acidification (148). 

Many of these reactions are reversible, and for the stronger nucleophiles they usually proceed the fastest. Typical examples are the addition of ammonia, amines, phosphines, and bisulfite. Alkaline conditions permit the addition of mercaptans, sulfides, ketones, nitroalkanes, and alcohols to acrylamide. Good examples of alcohol reactions are those involving polymeric alcohols such as poly(vinyl alcohol), cellulose, and starch. The alkaline conditions employed with these reactions result in partial hydrolysis of the amide, yielding mixed carbamojdethyl and carboxyethyl products. 

Sulfomethylation. The reaction of formaldehyde and sodium bisulfite [7631-90-5] with polyacrylamide under alkaline conditions to produce sulfomethylated polyacrylamides has been known for many years (44—46). A more recent pubHcation (47) suggests, however, that the expected sulfomethyl substitution is not obtained under the previously described strongly alkaline conditions of pH 10—12. This C-nmr study indicates that hydrolysis of polyacrylamide occurs and the resulting ammonia reacts with the NaHSO and formaldehyde. A recent patent claims a new high pressure, high temperature process at slightly acid pH for preparation of sulfomethylated polyacrylamide (48). 

Reaction with Other Aldehydes. Polyacrylamide reacts with glyoxal [107-22-2], C2H2O2, under mild alkaline conditions to yield a polymer with pendant aldehyde fiinctionahty. 

Formaldehyde condenses with itself in an aldol-type reaction to yield lower hydroxy aldehydes, hydroxy ketones, and other hydroxy compounds the reaction is autocatalytic and is favored by alkaline conditions. Condensation with various compounds gives methylol (—CH2OH) and methylene (=CH2) derivatives. The former are usually produced under alkaline or neutral conditions, the latter under acidic conditions or in the vapor phase. In the presence of alkahes, aldehydes and ketones containing a-hydrogen atoms undergo aldol reactions with formaldehyde to form mono- and polymethylol derivatives. Acetaldehyde and 4 moles of formaldehyde give pentaerythritol (PE) ... 

Under neutral or slightly alkaline conditions, only the unstable hemiformal (CH O—CH2OH, methoxymethan0I) is produced. Alpha-chloromethyl ether is synthesized from aqueous formaldehyde, methanol, and hydrogen chloride (54). However, under anhydrous conditions, a carcinogenic by-product, bis(chloromethyl)ether is also formed (55). 

Primary and secondary amines readily give alkylaminomethanols the latter condense upon heating or under alkaline conditions to give substituted methyleneamines (59). With ammonia, the important industrial chemical, hexamine, is produced. Tertiary amines do not react. 

Amphoteric Detergents. These surfactants, also known as ampholytics, have both cationic and anionic charged groups ki thek composition. The cationic groups are usually amino or quaternary forms while the anionic sites consist of carboxylates, sulfates, or sulfonates. Amphoterics have compatibihty with anionics, nonionics, and cationics. The pH of the surfactant solution determines the charge exhibited by the amphoteric under alkaline conditions it behaves anionically while ki an acidic condition it has a cationic behavior. Most amphoterics are derivatives of imidazoline or betaine. Sodium lauroamphoacetate [68647-44-9] has been recommended for use ki non-eye stinging shampoos (12). Combkiations of amphoterics with cationics have provided the basis for conditioning shampoos (13). 

Ethyleneknine dimer has been synthesized using catalytic amounts of an alkaU metal amide of ethyleneknine under alkaline conditions (89,90). 

The reaction of thioethers with ethyleneimine in the presence of acid yields sulfonium compounds. The reaction is reversible under alkaline conditions (125). Compounds in which double-bonded sulfur can exist in tautomerism with a form having a free SH group, such as thiourea (126,127), thiocarboxyhc acids (128), and thiophosphates (129), react to give aminoaLkylated products. The P-aminoethyl thiocarboxylate rearranges to give the amide. 

Derivatives. The most important data for 2-methyl a siridine and 1-(2-hydroxyethy1)asiridine, which previously had some industrial significance, are given in Table 1. Like ethyleneimine, these compounds ate used in polymer form and as intermediates. The use of activated asiridines, eg, /V-acylasiridines, for amino ethylation, under alkaline conditions, is of preparative interest (1). 

Reaction of MEK with ammonia and hydrogen produces j i -butylarnine, a fungistat and condensation with aUphatic esters under strongly alkaline conditions produces 1,3-diketones. 

Ma.nufa.cture. Isophorone is produced by aldol condensation of acetone under alkaline conditions. Severe reaction conditions are requited to effect the condensation and partial dehydration of three molecules of acetone, and consequendy raw material iaefftciency to by-products is limited by employing low conversions. Both Hquid- and vapor-phase continuous technologies are practiced (186,193,194). 

Divalent manganese compounds are stable in acidic solutions but are readily oxidized under alkaline conditions. Most soluble forms of manganese that occur in nature are of the divalent state. Manganese(Il) compounds are characteristically pink to colorless, with the exception of MnO and MnS which are green, and Mn(OH)2, which is white. The physical properties of selected manganese(Il) compounds are given in Table 6. 

A thermally stable, pure todorokite has been synthesized by autoclaving a layered stmctured manganese oxide, initially generated from the reaction of MnO and Mn " under alkaline conditions. The synthetic manganese oxide molecular sieve (11) was shown to have a tunnel size, ie, diameter of 690 pm. This material was thermally stable to 500°C just as natural todorokite is (68). 

This disproportionation is slow under less than molar alkaline conditions, and instantaneous under neutral or acidic conditions. The equiUbrium constant, iC, for the reaction at 25°C, is as follows (98) ... 

Under extremely alkaline conditions, pH > 12, potassium permanganate reacts involving a single-electron transfer, resulting in the formation of manganate (VI). 

Primary and secondary alcohols are readily oxidi2ed to aldehydes and ketones under alkaline conditions. Aldehydes, both aUphatic and aromatic, are converted into the corresponding carboxyUc acids. Ketones are generally oxidation resistant unless sufficient alkaU is present to effect enolization. The enol can be oxidatively cleaved. 

The methacrylates ate slightly to essentially nontoxic to fish and other aquatic species. Hydrolysis data suggest rapid breakdown at alkaline conditions, and studies show that MMA is ultimately biodegradable ia sewage sludge samples. Based on this information, the methacrylates ate not considered to be a significant environmental hazard. 

Phosphine has an 8-h time-weighted average exposure limit of 0.3 ppm (13). Under alkaline conditions the rate of PH formation is high. At neutral or acidic pH, the PH generation is slow but stiU very ha2ardous if the PH is allowed to accumulate in a confined vapor space. The safest commercial handling conditions for molten phosphoms are generally considered to be from pH 6 to 8 at 45—65°C. 

Pt—Q—Salt, [Pt(NH3)2(HP04)] and [Pt(OH)3] (259,260). Chloride-based baths have been superseded by P-Salt-based baths, which are more stable and relatively easily prepared. Q-Salt baths offer even greater stabiUty and produce hard, bright films of low porosity. Plating under alkaline conditions employs salts of [Pt(OH3)] . These baths are easily regenerated but have low stabiUty. Platinum films have uses in the electronics industry for circuit repair, mask repair, platinum siUcide production, and interconnection fabrication (94). Vapor deposition of volatile platinum compounds such as [Pt(hfacac)2] and... 

Oxidation of polysaccharides is a far more attractive route to polycarboxylates, potentially cleaner and less cosdy than esterification. Selectivity at the 2,3-secondary hydroxyls and the 6-primary is possible. Total biodegradation with acceptable property balance has not yet been achieved. For the most part, oxidations have been with hypochlorite—periodate under alkaline conditions. In the 1990s, catalytic oxidation has appeared as a possibiUty, and chemical oxidations have also been developed that are specific for the 6-hydroxyl oxidation. 

Under alkaline conditions, an amine addition reaction can occur. For example, in the reaction of C3H3CH2CH2NH2 and aEyl alcohol in the presence of sodium alcoholate at 108°C for 80 h, 43.4% A/-(3-hydroxypropyl)phenylethylamine is formed (12). 

---