Alkylbenzene sulphuric acids

Kinetic data are available for the nitration of a series of p-alkylphenyl trimethylammonium ions over a range of acidities in sulphuric acid. - The following table shows how p-methyl and p-tert-h xty augment the reactivity of the position ortho to them. Comparison with table 9.1 shows how very much more powerfully both the methyl and the tert-butyl group assist substitution into these strongly deactivated cations than they do at the o-positions in toluene and ferf-butylbenzene. Analysis of these results, and comparison with those for chlorination and bromination, shows that even in these highly deactivated cations, as in the nitration of alkylbenzenes ( 9.1.1), the alkyl groups still release electrons in the inductive order. In view of the comparisons just... 

Kilpatrick and Meyer163 measured the first-order rates of sulphonation of some alkylbenzenes by sulphuric acid at 12.3 °C. Rate coefficients were given graphically only and the parameters for the linear log (k x 106) versus —a+b [H2S04] plots (where the stoichiometric acid concentration is expressed in mole.l-1) were as follows, the acid range examined being given in parentheses ... 

An exceptionally badly reported kinetic study in which a linear correlation of rate coefficient with acidity function was claimed was that of Mackor et al. 11, who studied the dedeuteration of benzene and some alkylbenzenes in sulphuric acid-trifluoroacetic acid at 25 °C. Rates were given only in the form of a log rate coefficient versus —H0 plot and rate coefficients and entropies of activation (measured relative to p-xylene) together with heats of activation (determined over a temperature range which was not quoted) were also given (Table 129). However,... 

Aromatic nitro compounds that contain a side chain (e.g. nitro derivatives of alkylbenzenes) may be oxidised to the corresponding acids either by alkaline potassium permanganate (Aromatic hydrocarbons, Section 9.6.3, p. 1238) or, preferably, with a sodium dichromate-sulphuric acid mixture in which medium the nitro compound is more soluble. 

Much of the colour produced during sulphonation is contained in the spent acid. The upper layer in the separator, which contains around 90% alkylbenzene sulphonic acid (the remainder being primarily dissolved sulphuric acid) is also removed from the separator and neutralised with sodium hydroxide solution or with sodium carbonate solution to yield the active paste. When sodium hydroxide is used a considerable amount of heat must be removed. This is done in the third loop reactor of this process, the neutralisation heat exchanger (also known as the neutraliser). If sodium carbonate solution is used, the neutralisation is much less exothermic and no heat exchanger is needed at this stage. 

After sulphonation is complete, water is added to the acid products to achieve separation of the alkylbenzene sulphonic acid from sulphuric acid. The "spent acid" represents the lower (high gravity) phase and consists of 78% sulphuric acid, hi y coloured material and about 0.1 - 0.2% sulphonic acids. The separation is based on the principle that many sulphonic acids are relatively insoluble in sulphuric acid of intermediate strength (i.e. about 50 -80%) obtained by suitable dilution of the reaction mixture of sulphonic acid and sulphuric acid after sulphonation with 20% oleum or 100% sulphuric acid. This 70 - 80% sulphuric acid is unlike normal sulphuric acid especially with respect to colour, organic matter and viscosity. It has generally a dark brown/black colour and a strong odour of SO2. 

In the hydrolysing (stabilisation) step the organic anhydrides formed during sulphonation are convert with a small amount of water (about 0.3 to 1 % on sulphonic acid) to alkylbenzene sulphonic acid and traces of loosely chemical bound SO3 with water to form a small amount of sulphuric acid and reaction heat. The stabilisation tank should therefote i e. fitted with an agitator and coo g so that this post-reaction occurs jmder isothermal conditions. 

Follow the step by step operating procedures. Then, once the required preheating temperatures are reached (normally witiiin two hours), the plant will be ready for sulphur ignition sulphur dosing and sulphur igniter will be started, the conversion of SO2 SO3 will proceed from an initial 50% value to 98% and the sulphonation reaction with alkylbenzene will result in a partially-converted alkylbenzene sulphonic acid, to be returned to the off-spec circulation tank. 

The undiluted mixture from the sulphonation stage typically contains 60 - 70% alkylbenzene sulphonic acid, 30-40% sulphuric acid, about 1% water and up to 1% free oil. For the purpose of determining what separation will take place, the small amount of free oil may be neglected. Without free oil, a product post-sulphonation loop could have, for example, the following composition ... 

Figure 52 presents a phase diagram for the system alkylbenzene sulphonic acid - sulphuric acid -water. Before dilution, the sulphonation mixture is represented by a point (P) close to the bottom of the diagram, near or on the lower perimeter of the area of immiscibilily. In diluting with water the composition of the sulphonation mixture "moves up" into the area of immiscibility see dotted line P-L. After dilution into the area of immiscibility, the mixture of alkylbenzene sulphonic acid, sulphuric acid and water will separate into two phases a spent acid phase with very little sulphonic acid (about 0.3%) and a sulphonic acid phase. The composition of the latter is that of the intersection of the appropriate tie line (say the tie line indicated as 80% spent acid composition) with the left hand perimeter of the area of immiscibility (point R). The composition of the spent acid phase is given by the intersection of the same tie-line with the zero percent sulphonic acid line (see point S), since the small amount of sulphonic acid in the spent acid phase is neglected for the purpose of this phase diagram. From S, Q and R, all on the 80% spent acid tie-line, the composition of the sulphonic acid phase and the amounts of sulphonic and spent acid phases can be calculated. 

Different alkylbenzene qualities may present different phase diagrams and it may be necessary to determine the phase diagram in laboratory trials to arrive at the optimal conditions, i.e. a sulphonic acid phase with the minimum amount of sulphuric acid and water. 

The quality of alkylbenzene sulphonate from 20% oleum plants is normally very good. The free oil figures fall in a range between 0.6 and 1.7% on 100% AD. Due to the dissolved sulphuric acid in the sulphonic acid phase, the sodium sulphate levels on 1(X)% AD vary between 6 and 15% depending on the type of alkylate and the efficiency of the separation process of sulphonic acid/spent acid. Paste colour is normally very good, wiA values well below 1(X) Klett (5% AD solution, 4 cm cell, F42 filter). 

Determination of sulphuric acid in alkylbenzene sulphonic acids... 

The method described by Sak-Bosnar et al. [10] depends on the fact that the second hydrogen ion of sulphuric acid is significantly weaker than the first, and than the hydrogen ion of alkylbenzene sulphonic acid (and others). It is therefore possible to determine sulphuric acid in alkylben-... 

In both methods the titration to the first end-point measures the alkylbenzene sulphonic acid plus one hydrogen ion of the sulphuric acid. The additional titration to the second end-point measures the second hydrogen ion of the sulphuric acid. 

The book covers sulphonation of alkylbenzenes, primary alcohols, alcohol ethers, alpha-olefins and fatty acid methyl esters, with a strong emphasis on the sulphur-based SOs/air sulphonation technology. 

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