Cellulose alkaline conditions

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. 

A reactive dye—cellulose bond is subject to some slight hydrolysis during washing under alkaline conditions. 

Azoic dyeing of cellulosic fibres is a process that is used only to a small extent today. In this process, an azo pigment is formed by chemical reaction within the fibre. The cotton fibres are first impregnated with an appropriate coupling component such as the anilide of 3-hydroxy-2-naphthoic acid, 156, under aqueous alkaline conditions. The fibre is then treated with a solution of a stabilised diazonium salt, in which the... 

Vat dyes are insoluble in water and are applied to cellulosic fibres, usually with sodium dithionite under alkaline conditions, by a vatting process involving reduction to produce a... 

Scheme 7.19), leading to dyes with a 5-chloro-4-methyl-2-methylsulphonylpyrimidine reactive system (7.24). During reaction with the cellulosic fibre under alkaline conditions, the methylsulphonyl moiety is a particularly effective leaving group and rapid fixation takes place when the reactive system approaches the cellulosate anion. 

In the case of quaternary derivatives made from the non-planar aliphatic amines 7.64, 7.65 and 7.66, steric strains further destabilise the C-N+ bond so that reaction with cellulose occurs under alkaline conditions at 30 °C, whereas temperatures of about 40-50 °C are required for the pyridinium derivatives 7.67. The quaternisation approach appeared to offer the opportunity to prepare dyes yielding reactivity levels intermediate between those of aminochloro- and dichlorotriazine dyes without loss of the desirable stability of the dye-fibre bond to acidic conditions that is characteristic of aminohalotriazine dyes. Unfortunately, this ideal was not attainable because of the objectionable odours of the tertiary amines liberated by the fixation reaction and the sensitivity of the reactivity behaviour of the quaternised derivatives to the nature of the chromogen attached to the triazine ring, making it difficult to select compatible combinations of dyes. 

Polymeric pH indicators, phenolphthalein-formaldehyde (PPF) and o-cresolphthalein-formaldehyde (CPF) were synthesized with phenolphthalein and o-cresolphthalein reacted by formaldehyde under alkaline conditions, respectively. They can be immobilized in hydrolyzed cellulose diacetate membranes (HCDA) mainly due to macromolecular entrapment, and can be covalently bound to poly(vinyl alcohol) (PVA) via the considerable newly produced hydroxylmethyl groups [168,169], Phenol red (phenolsulfonphthalein) and its derivatives are commonly used for pH determination. 

McKelvey etal. (1959) investigated the reaction of epoxides with cellulose in alkaline conditions, reporting that alkaline cellulose reacted readily once the concentration of sodium hydroxide was sufficiently high. However, no evidence was found of reaction between cotton yarn and cellulose with a range of epoxides under a variety of reaction conditions. It was concluded that the apparent reactivity of cellulose with epoxides was primarily due to alkaline swelling of the cellulose, self-polymerization of the epoxide monomers then occurring within the interior structure of the fibres. It was also noted that the reactivity with phenol OH groups was very low (e.g. only 1 % conversion of ethylene oxide with various phenols). 

Anthraquinone vat dyes are water-insoluble dyes. They arc converted til leuco compounds (anthrahydroquinone.s) by reducing agents such as sodium hydrosulfite in alkaline conditions. These water-soluble leuco compounds have an affinity to cellulose fibers and penetrate them. After reoxidation by means of air or other oxidizing agents, the dye becomes water-insoluble again and fixes firmly on the fiber. 

Table I shows that aliphatic products in reaction liquors from both alkaline nitrobenzene and nitric acid oxidations have been largely neglected. The oligosaccharides listed were isolated from reaction of regenerated cellulose with oxygen under alkaline conditions. Table II lists references to the aromatic products isolated from the same three types of oxidations.

Scheme 8 Formation of acidic residues, stopping the peeling process of cellulose under alkaline conditions...

The "mild" NaBH4 reduction was done at 22°C (room temperature) and pH 8.0 The slightly alkaline conditions were necessary to maintain reasonable stability for the NaBH4 reagent. Sodium borohydride, 0.1 mL of 0.25 M NaBH4 in 0.1 M NaOH, was added to test solutions containing 1 mg of cellulose suspended in 0.785 mL of 0.1 M sodium phosphate, pH 8.0 Reaction mixtures were mixed and allowed to react for up to 90 min at room temperature. Reactions were terminated at selected times by the addition of 20 iL of 37% (w/v) HC1. Terminated reaction mixtures were typically allowed to stand for 30 min prior to neutralization by the addition of 95 pL of 2 N NaOH. Separate experiments showed that residual sodium borohydride could not be detected following the low-pH 30-min incubation period. 

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