Titration with benzethonium chloride

In setting a raw-material specification it may be adequate to specify the active content in millimol per 100 g, determined by an arbitrarily chosen titration method. In other cases it is necessary to determine at least olefin sulphonate and hydroxyalkane sulphonate separately. 

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When performing the two-phase titration with benzethonium chloride in alkaline medium and in the presence of phenolphthalein as indicator, not only the monosulfonates but also the di- and polysulfonates are determined [19]. The content of di- and polysulfonates is the difference between two titration results giving the amounts of total sulfonates and monosulfonates. Identifying the endpoint requires some experience. 

ISO 2869 [6] and ISO 2870 [7] deal with the determination of alkali-and acid-hydrolysable detergents respectively. ISO 2869 prescribes boiling 25 ml of a 0.003-0.005 M solution for 30 min with 5 ml of aqueous 10 M sodium hydroxide. ISO 2870 prescribes boiling a similar sample for 3h with 5 ml of aqueous 5M (490 g/1) sulphuric acid. In both cases the hydrolysed solution is neutralised and titrated with benzethonium chloride (see section 3.5). In the acid treatment, [H" ] is only 1.67 M, and this may be insufficient for complete hydrolysis of the more resistant titratable species. Both methods should be used where appropriate, but ISO 2870 may not be universally valid, and if it is used for products containing... 

If necessary, confirm the completeness of the deionisation as follows. Dissolve the residue from step 8 in chloroform and dilute to volume in a volumetric flask. Test a portion of this solution for the presence of whatever ionic surfactant predominated in the sample, e.g. by adding water and acid mixed indicator and titrating with benzethonium chloride. If the nonionic matter is not completely free of ionic surfactants, repeat the analysis using twice as much resin. 

These materials are readily determined by two-phase titration (ISO 2271) or potentiometric titration with benzethonium chloride. On acid hydrolysis they yield the corresponding alcohol, a sulphate ion and a hydrogen ion, and this affords three additional approaches—determination of the increase in acidity, of the amount of fatty alcohol or ethoxylated alcohol liberated, and of the sulphate ion. The experimental procedure may be varied within limits for example ISO 2870 [5] and ASTM D 1570-89 [6] differ with respect to the identity of the acid used, duration of boiling, choice of indicator and other details. The following procedures are similar to both of those standard methods. The choice of indicator is immaterial for these particular compounds, but is of crucial importance in some other cases. 

These materials can be titrated with benzethonium chloride, either by ISO 2271 or potentiometrically. 

Alkane sulphonates contain both mono- and disulphonates. The monosul-phonates can be determined by direct titration with benzethonium chloride according to ISO 2271, and this is the procedure recommended in ISO 6121 [13], but see the comment at the end of section 5.7.3. 

When the alkali titration per fraction falls to zero (after 10-12 fractions), change the eluent to methanol and continue collecting 10-ml fractions. Analyse by alkali titration, or by dilution and titration with benzethonium chloride. 

Note 3. For determination of the recovered mono- and disulphonic acids the authors recommended passing the pure ammonium salts obtained at step 8 through the cation exchanger and titrating with potassium hydroxide to bromocresol purple. The monosulphonates but not the disulphonates can also be determined by titration with benzethonium chloride. 

Alkene monosulphonates may be extracted as the sulphonic acids from strongly acid solution and determined by titration with alkali. Under these conditions the hydroxyalkane sulphonates are converted back to the sultones from which they were derived, and although these are also extracted, they are not titrated by alkali. Alternatively the alkene sulphonates in the extract may be titrated with benzethonium chloride. The hydroxyalkane sulphonates may be determined by alkaline hydrolysis followed either by measurement of the alkali consumed or by a second titration with benzethonium chloride. The following method is adapted from those of Ranky and Battaglini [20] and Martinsson and Nilsson [21]. The alkali used for hydrolysis of the sultones is alcoholic simply to prevent excessive foaming. 

As a check, the sum of the alkene sulphonates and hydroxyalkane sulphonates in mol/1 may be determined on the original sample by titration with benzethonium chloride. The result includes any 2-hydroxy-alkane sulphonate, which is not converted to the sultone by the acid treatment described, and so may differ slightly from the sum of the... 

The active content of acyl isethionates in raw materials and products is determined either by titration with benzethonium chloride or by saponification. The fatty acid may be extracted after acidification for molecular-... 

Titration with benzethonium chloride in acid solution measures the sulphonated ester plus the sulphonated carboxylic acid, only the sulphon-ate group of the latter being titrated. In alkaline solution the titration measures the sulphonated ester plus twice the sulphonated carboxylate, both the sulphonate and the carboxylate group being titrated. Alpha-sulphonated esters give poor potentiometric titration curves, and two-phase titration is strongly preferred. 

The ester cannot be determined by saponification because this slowly removes the sulphonate group as well as hydrolysing the ester group. It can be determined by acid hydrolysis followed by measurement of the a-sulphonated carboxylate salt produced, either by potentiometric titration of the weak acid or by two-phase titration with benzethonium chloride. Both procedures measure the a-sulphonated ester plus the unsulphonated ester. If the latter is present at a significant level, it can be determined (section 5.11.2) and corrected for. 

Mono- and dialkylsulphosuccinate may be determined by two-phase titration with benzethonium chloride. Materials made by the sodium... 

One mol of aspartate reacts with 1 mol of mono- or dialkylsulphosuccin-ate when the latter is titrated with benzethonium chloride in acid solution. One mol of aspartate consumes 1 mol of acid when titrated, and/or 2 mol of alkali during alkaline hydrolysis. 

All may be determined by two-phase or potentiometric titration with benzethonium chloride. Titration of sulphosuccinamates in acid solution measures the sulphonate group alone (but see section 5.13.3), and titration in alkaline medium measures the carboxylate group as well (cf. section 5.11.3). Sulphosuccinamates, possessing a carboxylate group, can also be determined by potentiometric acid-base titration. 

Soaps, sarcosinates and alkylether carboxylates (ethoxycarboxylates, polyethylene glycol monoesters) give poor curves in potentiometric titrations with benzethonium chloride, and ISO 2271 in alkaline solution does not always work very well for these compounds, particularly those of shorter chain length. The bromophenol blue method works well provided that the solution is distinctly alkaline it is necessary to add 5 ml 0.1 M sodium hydroxide before titrating. 

Fatty acids and acyl sarcosines may be extracted with petroleum or diethyl ether from an acidified aqueous solution if no other surfactants are present, or with petroleum ether from acidified 50% ethanol if they are. The extract is evaporated and the residue weighed. Alkylether carboxylic acids cannot be quantitatively extracted with petroleum ether. They can be extracted from aqueous solution with chloroform, but they are best determined by two-phase titration with benzethonium chloride in akaline solution (bromophenol blue method) or direct potentiometric acid-base titration. 

The free fatty acid can be directly determined by two-phase titration with benzethonium chloride, in which case the presence of basic catalyst is irrelevant. Bares and Zajic [17] used this approach, with bromocresol green as indicator, and taking as the end-point the final disappearance of colour from the aqueous layer. A blank test was necessary. They showed that quantitative titration only occurred when the pH was at least 11.3. The bromophenol blue method would serve equally well. 

B. Titration with benzethonium chloride in alkaline solution. The solution must be at least 0.1 M in hydroxide ion. Potentiometric titration is preferred, and the bromophenol blue method is probably better than the mixed indicator procedure. The present author s limited experience suggests that WW amphoterics are titrated rather more successfully as cationics than as anionics. 

SW sulphobetaines are more like anionics than cationics, and can be titrated with benzethonium chloride in alkaline solution, by either two-phase or potentiometric procedures. They cannot be titrated with NaTPB. 

All sulphate and sulphonate anionics except hydrocarbon sulphonates can be acid-hydrolysed. In every case but one, namely a-sulphonated fatty esters, the hydrolysis destroys their surface activity and renders them incapable of titration with benzethonium chloride. In that exceptional case, the titration per molecule is doubled by the hydrolysis. All esters are decomposed by alkaline hydrolysis or saponification, but in the case of a-sulphonated fatty esters this is not a useful measurement because of the slow hydrolysis of the sulphonate group. Also, alkanolamides, particularly dialkanolamides, are hydrolysed slowly by the normal saponification process, and although this is not a useful method of analysis for them, the possibility of generating measurable amounts of soap and alkanolamine cannot be ignored when alkali-hydrolysing anionic esters. 

Anions of strong acids undergo titration with benzethonium chloride at all pHs. Anions of weak acids do so only in alkaline solution. 

In all cases the first action is to determine total activity by titration with benzethonium chloride (BEC), and this is to be taken as mandatory in each of the following cases. After acid hydrolysis a second BEC titration to determine the sulphonated hydrocarbon is probably all that is required in the majority of cases, but the following are alternatives. In the case of a-sulphonated fatty esters, the second BEC titration measures the total a-sulphonated fatty acid plus the sulphonated hydrocarbon (see below). 

Assay is conventionally performed by two-phase or one-phase titration with benzethonium chloride, as described in Chapter 16. Assay may also be performed by determination of... 

The content of sulfatosulfonates can be estimated by measuring the active agent content by titration with benzethonium chloride before and after acid hydrolysis. Hydrolysis converts the sulfatosulfonates to hydroxyalkane sulfonates, which add to the assay value (81). 

A modification of two-phase titration calls for preparing only one titration system for both cationics and anionics the benzethonium chloride, disulfine blue/dimidium bromide method which is standard for anionics. For the determination of cationics, an excess of standard sodium dodecylsulfate is added, and the excess determined by titration with benzethonium chloride (31). 

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