Sulphonic acid phase

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. 

H2SO4 carry-over in sulphonic acid phase (weight %)... 

The sulphonic acid phase leaves the separator at the top, the spent acid phase at the bottom. 

Good separation between the sulphonic acid and the spent acid is important, in order to minimise the loss of sulphonic acid in the spent acid phase. Also, the higher the sulphuric acid content of the sulphonic acid phase, the less acceptable the latter is for many of its applications. Furthermore, the higher the sulphonic acid content of the spent acid, the less acceptable this is to its prospective buyers, because of foam formation in fruther processing. 

The cross-sectional area of the separator should be 1 m per ton AD/h. To ensure good separation, the sulphonic acid phase should remain in the separator for about 60 minutes. All the pipework should preferably be made of mild steel lined with PTFE. 

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). 

If in the last phase the different sulphonic acids of /d-naphthol are employed, arious shades of red, known as Crocci7is ate produced. Thus it appears that the colour deepens from orange to led with the introduction of a second azo-group. 

Many racemic mixtures can be separated by ordinary reverse phase columns by adding a suitable chiral reagent to the mobile phase. If the material is adsorbed strongly on the stationary phase then selectivity will reside in the stationary phase, if the reagent is predominantly in the mobile phase then the chiral selectivity will remain in the mobile phase. Examples of some suitable additives are camphor sulphonic acid (10) and quinine (11). Chiral selectivity can also be achieved by bonding chirally selective compounds to silica in much the same way as a reverse phase. A example of this type of chiral stationary phase is afforded by the cyclodextrins. 

One potentially important example of CIDNP in products resulting from a radical pair formed by electron transfer involves a quinone, anthraquinone j5-sulphonic acid (23). When irradiated in the presence of the cis-syn dimer of 1,3-dimethylthymine (24), enhanced absorption due to vinylic protons and emission from the allylic methyls of the monomer (25) produced can be observed (Roth and Lamola, 1972). The phase of the polarizations fits Kaptein s rules for intermediate X... 

The role of a second liquid phase in photochemical sulphoxidation of paraffins with SO2 and O2 mixtures may also be cited, where water is used to extract sulphonic acid to prevent formation of di- and poly-sulphonic acids (Fischer, 1978). 

Fig. 3.3f(/) shows the use of a combination of ion-pairing and ion-suppression to separate a mixture of acids and bases. The pH of the mobile phase is about 2.5, as at this pH the maleic acid is unionised and elutes quickly as a very polar molecule on the reverse phase column. The other solutes are all weak bases which at pH 2.5 are fully protonated and pair with the pentane sulphonic acid anion. 

Column C-18 mobile phase CH3OH /H O 50 50 + heptane sulphonic acid (pH about 3.5). 

The sulphurous acid liberated in the second phase of the process by the addition of hydrochloric acid hydrogenates the azo-double bond, probably via an addition product A, of which one S03H-group is easily removed by hydrolysis with the formation of the sodium salt of phenylhydrazine sulphonic acid. 

Counter-ions which are frequently used include tetrabutylammonium phosphate for the separation of anions and hexane sulphonic acid for cations. The appropriate counter-ions are incorporated in the solvent, usually at a concentration of about 5 mmol 1" and the separation performed on the usual reverse phase media. This ability to separate ionic species as well as non-polar molecules considerably enhances the value of reverse-phase chromatography. 

Fig. 3.107. Comparison of micro-HPLC separations of aromatic sulphonic acids in different mobile phases (a) 0.005 M tetrabutylammonium hydrogensulphate (TBAS) in 15 per cent (v/v) methanol in water (1) Laurent acid, (2) amino-F-acid, (3) Cleve-1,6- and Peri acids, (4) unidentified impurity, (5) Cleve-1,7-acid and (6) unidentified impurity, (b) 0.005 M tetrabutylammonium hydrogensulphate (TBAS) in 15 per cent (v/v) methanol in water with 0.01 M /Lcyclodextrin (CD) (1) Laurent acid, (2) amino-F-acid, (3) Cleve-1,6-acid, (4) Peri acids, (5) unidentified impurity, (6) Cleve-1,7-acid and (7) unidentified impurity. Column, Biosphere Si C18, 162 X 0.32 mm i.d. flow rate 5 pl/min, column temperature ambient, detection, UV, 220-230 nm. Reprinted with permission from P. Jandera et al. [164].

KOH (2.8 g) and K2SO, (8.1 g) in HzO (25 ml) is added to the activated chloroarene (25 mmol) and TBA-HS04 (17.3 g, 50 mmol) in CH2C12 (50 ml), which immediately becomes blue-red. The mixture is refluxed for 1 h. The organic phase is separated, Ba(C104)2 (12 g) in H20 (15 ml) is added, and the mixture is stirred to precipitate the barium salt of the sulphonic acid, which is washed with CH2CI2 (10 ml) and dried over... 

Although there are other convenient procedures for the conversion of sulphides into sulphoxides and sulphones, the phase-transfer catalysed reaction using Oxone has the advantage that the oxidation can be conducted in the presence of other readily oxidized groups, such as amines, alkenes, and hydroxyl groups, and acid-labile groups, such as esters and carbamates [6, 7], Hydrolysis of very acid-labile groups, such as ketals, can result in production of the keto sulphone. 

KI (8.0 g, 48 mmol) and TBA-I (0.58 g, 1.5 mmol) are added to the sulphonic acid (6 mmol) and ethyl polyphosphate or polyphosphoric acid (48 mmol) [or P4O 0 (36 mmol)] in the appropriate solvent (20 ml) (CHC13 for ethyl polyphosphate sulpholane for polyphosphoric acid MeCN for P4O10) and stirred under reflux for ca. 5 h. H20 (10 ml) is added and the mixture is refluxed for a further 1 h and then poured into PhH (100 ml). The organic phase is separated, washed with H20 (3 x 50 ml) and aqueous Na2S203 (0.5M, 2 x 100 ml), dried (Na2S04), and evaporated to yield the disulphide. 

Numerous assays are also available in the literature for analysis of biogenic amines and their acid metabolites in brain tissue. For example, Chi and colleagues (1999) developed a rapid and sensitive assay for analyzing NE, DA, 5-HT, 5-hydroxyindole-3-acetic acid (5-HIAA), and homovanilHc acid (HVA) in rat brain. The assay used a C18 column (150 x 4.6 mm) coupled to an amperometric electrochemical detector. The mobile phase consisted of a phosphate buffer (pH 4.75) and octane sulphonic acid as an ion-pair reagent in acetonitrile. The sensitivity of the analytes reported was 3-8 pg on column. 

Buffered mobile phases are inherently used to adjust and control the adsorption-desorption process. These CSPs are especially useful for the separation of very polar charged analytes, such as sulphonic acids. Chiral anion-exchangers are the most successful CSPs and among them the cinchona alkaloids, quinine and quinidine (Figure... 

Solvent extraction has become a common technique for the determination of formation constants, P , of aqneons hydrophilic metal complexes of type MX , particularly in the case when the metal is only available in trace concentrations, as the distribntion can easily be measnred with radioactive techniques (see also section 4.15). The method reqnires the formation of an extractable complex of the metal ion, which, in the simplest and most commonly used case, is an nn-charged lipophilic complex of type MA. The metal-organic complex MA serves as a probe for the concentration of metal ions in the aqueous phase through its equilibrium with the free section 4.8.2. This same principle is used in the design of metal selective electrodes (see Chapter 15). Extractants typically used for this purpose are P-diketones like acetylacetone (HAA) or thenoyltrifluoroacteone (TTA), and weak large organic acids like dinonyl naph-talene sulphonic acid (DNNA). 

Why is the octane sulphonic acid included in the mobile phase ... 

---