Aromaticity tests

EPA. 1982i. Purgeable aromatics. Test method - method 602. Cincinnati, OH U.S. Environmental Protection Agency, Environmental Monitoring Systems Laboratory. 

The aromatics tested (Tables 3-4 and 3-5) normally exhibit a levelling of the TGA curve at weight (mass) losses more than 85-95 %. There is doubt whether this is a real pyrolysis because the point of inflexion is in the range from 230 °C up to 300 °C. Nevertheless the length of an aliphatic side chain influences the thermal behavior of substituted pyrenes... 

The aromatics tested displayed melting temperatures somewhat lower than the values from the references (Table 3-10). The average of the deviations amounts to -2.2 %. 

Aromatics test C j-C 8 packing hy-drophobic interaction, selectivity benzene, naphthalene, fluorene, anthracene, benzanthracene acetonitrile - water, 75 25 wt % UV (254 nm)... 

Composition is normally expressed by a distillation curve, and can be supplemented by compositional analyses such as those for aromatics content. Some physical properties such as density or vapor pressure are often added. The degree of purity is indicated by color or other appropriate test (copper strip corrosion, for example). 

The isolation of an aliphatic acid from its aqueous solution, particularly in the presence of metallic salts, is a tedious operation (cf. p. 56), although a few such acids, e.g., succinic acid, can be extracted with ether. Since, however, a solution of an acid or one of Its salts is admirably suited for most of the tests in this series, the isolation of the free acid is rarely necessary except as a nieans of distinguishing (as in (i)) between aliphatic and aromatic members. 

The aliphatic hydrocarbons are extremely unreactive and do not respond to any of the following tests for aromatic hydrocarbons. 

To 5 ml. of water add 1-2 drops of the amine if the amine does not dissolve, add a drop or two of concentrated hydrochloric acid. Add 0-5-1 ml. of this amine solution to 2-3 ml. of the reagent an almost immediate precipitate indicates the presence of a primary amine. A slight turbidity indicates the presence of a primary amine as an impurity. (Primary aromatic amines generally require 2-3 minutes for the test. Urea and other amides, as well as amino acids, do not react.)... 

SULPHONATION OF AROMATIC AMINES If aniline is treated with excess of concentrated sulphuric acid and the resulting mixture, which contains aniline sulphate, is heated at 180° until a test portion when mixed with sodium hydroxide solution no longer liberates aniline, p-aminobenzenesulphonic acid or sulphanilic acid is formed this separates as the dihydrate upon pouring the cooled mixture into water. The reaction prohahly proceeds as follows ... 

Primary aromatic amines differ from primary aliphatic amines in their reaction with nitrous acid. Whereas the latter yield the corresponding alcohols (RNHj — ROH) without formation of intermediate products see Section 111,123, test (i), primary aromatic amines 3neld diazonium salts. Thus aniline gives phcnyldiazonium chloride (sometimes termed benzene-diazonium chloride) CjHbNj- +C1 the exact mode of formation is not known, but a possible route is through the phenjdnitrosoammonium ion tlius ... 

Aromatic aldehydes react with the dimedone reagent (Section 111,70,2). All aromatic aldehydes (i) reduce ammoniacal silver nitrate solution and (ii) restore the colour of SchifiF s reagent many react with sodium bisulphite solution. They do not, in general, reduce Fehling s solution or Benedict s solution. Unlike aliphatic aldehydes, they usually undergo the Cannizzaro reaction (see Section IV,123) under the influence of sodium hydroxide solution. For full experimental details of the above tests, see under Ali-phalic Aldehydes, Section 111,70. They are easily oxidised by dilute alkaline permanganate solution at the ordinary temperature after removal of the manganese dioxide by sulphur dioxide or by sodium bisulphite, the acid can be obtained by acidification of the solution. 

An additional useful test is to distil the acid or its sodium salt with soda lime. Heat 0.5 g. of the acid or its sodium salt with 0 2 g. of soda lime in an ignition tube to make certain that there is no explosion. Then grind together 0-5 g. of the acid with 3 g. of soda hme, place the mixture in a Pyrex test-tube and cover it with an equal bulk of soda hme. Fit a wide dehvery tube dipping into an empty test-tube. Clamp the tube near the mouth. Heat the soda lime first and then the mixture gradually to a dull-red heat. Examine the product this may consist of aromatic hydrocarbons or derivatives, e.g., phenol from sahcyUc acid, anisole from anisic acid, toluene from toluic acid, etc. 

Group VI. Concentrated sulphuric acid provides a simple test for the diflferentiation inter alia between (a) saturated paraffin and cyclic hydrocarbons and also simple aromatic hydrocarbons and (b) unsaturated hydrocarbons. 

Fuming sulphuric acid test. Place 2 ml. of 20 per cent, fuming sulphuric acid in a dry test-tube, add 0 -5 ml. of the hydrocarbon and shake vigorously. Only the aromatic hydrocarbon dissolves completely heat is evolved, but excessive charring should be absent. 

The most common interfering substance, especially with alcohols of low mole cular weight, is water this may result in an inaccurate interpretation of the test if applied alone. Most of the water may usually be removed by shaking with a little anhydrous calcium sulphate,. though dry ethers (and also the saturated aliphatic and the simple aromatic hydrocarbons) do not react with sodium, many other classes of organic compounds do. Thus ... 

Sulphinic acids. Aromatic sulphinic acids are found in Solubility Group II. They may be detected by dissolving in cold concentrated sulphuric acid and adding one drop of phenetole or anisole when a blue colour is produced (Smiles s test), due to the formation of a para-substituted aromatic sulphoxide. Thus the reaction with benzenesulphinic acid is ... 

The applicability of the two-parameter equation and the constants devised by Brown to electrophilic aromatic substitutions was tested by plotting values of the partial rate factors for a reaction against the appropriate substituent constants. It was maintained that such comparisons yielded satisfactory linear correlations for the results of many electrophilic substitutions, the slopes of the correlations giving the values of the reaction constants. If the existence of linear free energy relationships in electrophilic aromatic substitutions were not in dispute, the above procedure would suffice, and the precision of the correlation would measure the usefulness of the p+cr+ equation. However, a point at issue was whether the effect of a substituent could be represented by a constant, or whether its nature depended on the specific reaction. To investigate the effect of a particular substituent in different reactions, the values for the various reactions of the logarithms of the partial rate factors for the substituent were plotted against the p+ values of the reactions. This procedure should show more readily whether the effect of a substituent depends on the reaction, in which case deviations from a hnear relationship would occur. It was concluded that any variation in substituent effects was random, and not a function of electron demand by the electrophile. ... 

Something interesting happens when we go beyond benzene to apply the aromatic ring current test to annulenes... 

Aromatic and Nonaromatic Hydrocarbon Separation. Aromatics are partially removed from kerosines and jet fuels to improve smoke point and burning characteristics. This removal is commonly accompHshed by hydroprocessing, but can also be achieved by Hquid-Hquid extraction with solvents, such as furfural, or by adsorptive separation. Table 7 shows the results of a simulated moving-bed pilot-plant test using siHca gel adsorbent and feedstock components mainly in the C q—range. The extent of extraction does not vary gready for each of the various species of aromatics present. SiHca gel tends to extract all aromatics from nonaromatics (89). 

Specifications also appear in other pubHcations, including pubHcations of the Fragrance Materials Association (FMA) of the United States (53,57) (see also Fine chemicals). The FMA specifications include essential oils, natural flavor and fragrance materials, aromatic chemicals, isolates, general tests, spectra, suggested apparatus, and revisions adopted by the FMA. 

The high fluorine content contributes to resistance to attack by essentially all chemicals and oxidizing agents however, PCTFE does swell slightly ia halogenated compounds, ethers, esters, and selected aromatic solvents. Specific solvents should be tested. PCTFE has the lowest water-vapor transmission rate of any plastic (14,15), is impermeable to gases (see also Barrierpolymers), and does not carbonize or support combustion. 

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