Chlorinated phenols points

Non-point sources of 2,4-dichlorophenol and 2,4,5-trichlorophenol are mainly agricultural, since the phenoxy herbicides are hydrolyzed back to the phenols with a lifetime of about a week near 20°C. A minor local source of chlorophenols is chlorination of raw drinking water, which is contaminated with phenol (see Chapter 10). The most important chlorinated phenol is the pentachloro congener. 

Figure 2. A plot of sensor response versus the melting points of chlorinated phenols.

The (9-cresol novolaks of commercial significance possess degrees of polymerization, n, of 1.7—4.4 and the epoxide functionaUty of the resultant glycidylated resins varies from 2.7 to 5.4. Softening points (Durran s) of the products are 35—99°C. The glycidylated phenol and o-cresol—novolak resins are soluble in ketones, 2-ethoxyethyl acetate, and toluene solvents. The commercial epoxy novolak products possess a residual hydrolyzable chlorine content of <0.15 wt% and a total chlorine content of ca 0.6 wt % (Table 2). 

Concentration profiles for compound 67 are given in Figure 7. Although the relative effect of dispersion due to tidal flow and downstream movement due to the net river flow are not precisely known, it is clear from these data that compound 67 comes from a point source located near river mile 100. In fact, the company which produces the precursor alcohols (no. 68-70), the chemically related chlorinated ethylene glycol (no. 64) and the Cg-phenol (no. 38) discharges its effluent at river mile 104. 

Reactions. -Hydroxybenzoic acid undergoes the typical reactions of the carboxyl and hydroxyl moieties. When heated above its melting point, it decomposes almost completely into phenol and carbon dioxide. It reacts with electrophilic reagents in the predicted manner and does not undergo the Friedel-Crafts reaction. Nitration, halogenation, and sulfonation afford the 3-substituted products. Heating -hydroxybenzoic acid with 8 IV-nitric acid results in a 95% yield of picric acid. In a similar fashion, treatment with chlorine water yields 2,4,6-trichlorophenol (50). 

It is reported that an industrial explosion was initiated by charging potassium hydroxide in place of potassium carbonate to the chloro-nitro compound in the sulfoxide [1], Dry potassium carbonate is a useful base for nucleophilic displacement of chlorine in such systems, reaction being controlled by addition of the nucleophile. The carbonate is not soluble in DMSO and possesses no significant nucleophilic activity itself. Hydroxides have, to create phenoxide salts as the first product. These are better nucleophiles than their progenitor, and also base-destabilised nitro compounds. Result heat and probable loss of control. As it nears its boiling point DMSO also becomes susceptible to exothermic breakdown, initially to methanethiol and formaldehyde. Methanethiolate is an even better nucleophile than a phenoxide and also a fairly proficient reducer of nitro-groups, while formaldehyde condenses with phenols under base catalysis in a reaction which has itself caused many an industrial runaway and explosion. There is thus a choice of routes to disaster. Industrial scale nucleophilic substitution on chloro-nitroaromatics has previously demonstrated considerable hazard in presence of water or hydroxide, even in solvents not themselves prone to exothermic decomposition [2],... 

It is of esjx cial importance to know the potential interval within which one or several distinct reactions take place. The determination of this depends upon the change in potential which the presence of a depolarizer produces as opposed to an electrolyte containing no depolarizer. For example, if it is desired to learn if chlorine derivatives of phenol can be prepared at the anode by electrolysis of a hydrochloric-acid solution of phenol, then the point of decomposition of the chlorine ion, in combination with the hydrogen electrode, is found at LSI volts in a l/i n-hydrochloric-acid solution. If phenol is added to this solution, the break in the curve occurs already at 0.1) volt.2 Therefore the span in potential, within which the reaction for the formation of chlorine derivatives of phenol must take place, lies between 0.9 and 1.3 volts. In thin manner Dony-H6nault, among others, determined the decomposition potential of the OH ions, in combination with the hydrogen electrode, in dilute sulphuric-acid solution both without and with the addition of ethyl alcohol. He found... 

As shown by the downward swing of the curve, the reactions that occur between point B and the breakpoint are all breakdown reactions. Snbstances that have been formed before reaching point B are destroyed in this range of dosage of chlorine. In other words, the chloro-organics that have been formed, the organic chloramines that have been formed, the ammonia chloramines that have formed, and all other snbstances that have been formed from reactions with compounds such as phenols and fnlvic acids are all broken down within this range. These breakdown reactions have been collectively called breakpoint reactions. 

Organic materials are generally removed by addition of powdered activated carbon. The carbon may be added at any point in the plant, although it is advantageous to have as much contact as possible. The adsorption reaction is slow at room temperature, since it is diffusion-controlled. Oxidation with chlorine, potassium permanganate, or ozone may destroy tastes and odors or it may intensify them, depending upon the particular compounds involved. For example, chlorination of phenolic compounds leads to gready increased tastes and odors. For this reason, the system must be studied in the laboratory prior to water treatment. 

In contrast to aliphatic alcohols, which are mostly less acidic than phenol, phenol forms salts with aqueous alkali hydroxide solutions. At room temperature, phenol can be liberated from the salts even with carbon dioxide. At temperatures near the boiling point of phenol, it can displace carboxylic acids, e.g. acetic acid, from their salts, and then phenolates are formed. The contribution of ortho- and -quinonoid resonance structures allows electrophilic substitution reactions such as chlorination, sulphonation, nitration, nitrosation and mercuration. The introduction of two or three nitro groups into the benzene ring can only be achieved indirectly because of the sensitivity of phenol towards oxidation. Nitrosation in the para position can be carried out even at ice bath temperature. Phenol readily reacts with carbonyl compounds in the presence of acid or basic catalysts. Formaldehyde reacts with phenol to yield hydroxybenzyl alcohols, and synthetic resins on further reaction. Reaction of acetone with phenol yields bisphenol A [2,2-bis(4-hydroxyphenyl)propane]. 

Some researchers pointed out that extracted humic materials might cause problems for the extraction and photolysis of probe (pollutant) molecules. First, the extraction efficiency may decrease, and second, humics are known to quench photochemical reaction. For example, Zepp R..G. et al. (1975) suggested that phenolic humic substances present on most inland waters could inhibit free radical chain reactions. Thus, quantum yields for direct photolysis of chlorinated compounds in the aquatic environment are not likely to exceed unity. 

Other reactions on chlorinated nanodiamonds include radical reactions with cresols and related alkylaromatic compounds. p-Cresol, for instance, allows for the introduction of terminal phenolic groups that may serve as valuable starting-point for the incorporation into polymers (Section 5.5.2.9) or for the attachment of biologically active moieties. 

The use of a solvent to extract phenol from carbon has been more successful. Mackert53 percolates benzene through the carbon bed to displace the phenol and water from the carbon. The phenol collects in the benzene layer and is subsequently separated by distillation. The benzene remaining on the carbon is removed by low-pressure steam. Other eluting solvents that have been employed are alcohol, chlorinated hydrocarbons, low-boiling-point esters, ammonia, and sodium hydroxide. 

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