CS260208B1 - A method for determining free phenol or cresols in condensation products of these compounds with aldehydes and optionally polyamines - Google Patents

Abstract

The solution simplifies and accelerates the analytical procedure without negatively affecting the accuracy and reproducibility of the results, and allows its use in operational practice. It consists in the fact that a solution of the analyzed condensation product in an organic solvent is applied in a strip to the start of the chromatography plate, which is developed by the action of a mixture containing 40 to 90 vol. % hexane and 60 to 10 vol. % ethyl acetate. A comparative chromatogram developed on the same plate under the same conditions and subjected to detection with a reagent for substances of phenolic nature determines the position of the group of separated phenol or cresols, the part of the plate with the strip of these substances is separated, extracted with water and the phenol or cresols in the extract are determined photometrically.

Description

The invention relates to a method for the determination of free phenol or cresols in their condensation products with aldehydes and optionally polyamines.

One group of these condensation products can include phenolic resins, forming a very important group of substances today, which are used in a wide variety of industries. Resols represent a mixture of low- to medium-molecular isomeric phenol-formaldehyde condensation products (monomers, oligomers to polymers) and the remaining unreacted components. The same applies to novolaks except that the main product is a higher molecular weight linear polymer. Knowledge of the residual phenol content is desirable both in monitoring the production of phenolic resins and in characterizing them as the end product in relation to their properties. Another group is the amine hardeners of epoid resins formed by the condensation of cresols with aldehydes and polyamines, which are preferably used in the application of these materials in the construction industry.

Procedures ranging from classical analysis to modern instrumental physicochemical methods such as infrared spectra260 208 scopia, nuclear magnetic resonance, gas and liquid chromatography and their association with mass spectrometry, gel permeation chromatography and others can be used to characterize these condensation products. Classical methods are lengthy and laborious, instrumental methods require expensive instrumentation or highly qualified operators. All of these circumstances are against the use of these procedures in normal operating practice. Thin layer chromatography or paper chromatography can also be used to determine phenol in phenol-formaldehyde resins. Phenol is determined by cutting out the portion of the chromatogram containing the phenol spot and weighing or measuring the area of the spot and calculating the quantity from the logarithm of the phenol concentration. Both methods are unreliable because they require a precise delimitation and delimitation of the spots on the chromatogram, which is not practically possible by the nature of surface chromatography. In addition, prior art processes for paper or thin-layer chromatography of phenol-formaldehyde resins use mobile phases containing toxic, irritant or otherwise harmful substances such as methanol, benzene, acetic acid, chloroform, ammonia, and others, which is undesirable in occupational safety laboratories .

The present invention is directed to a method for determining free phenol or cresols in the condensation products of these compounds with aldehydes and optionally polyamines by thin layer chromatography using a mixture of hexane and ethyl acetate as eluent. SUMMARY OF THE INVENTION Firstly, a strip of a solution of the evaluated condensation product in an organic solvent is applied to the start of the chromatography plate and the chromatogram is developed in a mixture consisting of 40 to 90% by volume hexane and 60 to 10% by volume ethyl acetate. This separates phenol or cresols from the other components. A portion of the strip with these separated compounds is then separated, extracted with water, and the phenol or cresols contained in the aqueous extract are determined by spectrophotometry. The position of the strip of separated compounds on the plate is determined from a reference chromatogram that develops on the same plate under the same conditions, then separated and subjected to reagent detection for phenolic substances.

The process according to the invention is advantageous in that several samples can be processed at the same time, ie it is faster than the methods used hitherto. It does not require special or expensive instrumentation, provides sufficiently accurate, correct and reproducible results and uses mixtures of non-toxic chemicals to dissolve samples and develop chromatograms. This makes it suitable not only for laboratories, but also for operational practice.

For the determination of free phenol or cresols by the process according to the invention, it is usually carried out by treating a solution of the appropriate condensation product of known concentration in a suitable volatile solvent (generally conventional ethanol denatured with toluene, a mixture of denatured ethanol and acetone; methanol alone) is applied in a lane to the start of the chromatographic plate, leaving a portion (about 1-2 cm) at the edge of the start free. Place the same sample for the reference chromatogram on this vacant space. After developing the entire plate in hexane-ethyl acetate (40:60 to 90:10 v / v) and drying, part of the plate with the dotted reference chromatogram is separated or the remaining part of the plate is covered and the comparative chromatogram is called up by any conventional method for aromatic compounds. phenol, preferably by spraying a mixture of 1.5% aqueous ferric chloride and potassium ferrocyanide in a 1: 1 ratio by volume or 1% acetone with a solution of p-nitrobenzenediazonium fluoroborate. Depending on the position of the phenol or cresol spot in this comparative chromatogram, a strip corresponding to the elution band of 208 208 h of these compounds is excised from the remainder of the plate. The strip is placed in a container (eg a flask or beaker) so that it is completely submerged by subsequent coating of a known amount of water, or the strip can be cut into smaller pieces before being transferred to the container. Thereafter, the phenol or cresols are allowed to be extracted from the thin layer into the added water under gentle stirring or by standing with occasional shaking for a minimum of 10 minutes. In an aliquot of this aqueous extract, the compounds are / isophotometrically against a blank or distilled water by any conventional method, e.g. after reaction with 4-aminoantipyrine in an alkaline medium in the presence of potassium ferrocyanide. Reagent solutions are prepared on the same day they are to be used. The concentration of phenol or cresols in the sample solution is then calculated using the calibration dependence obtained from solutions of these substances of known concentration, processed in the same manner as in the sample analysis. The found calibration dependence is linear, it goes through the ecm, so the procedure is not burdened by a constant error. The mean results from the three parallel determinations do not differ significantly in the significance level of 0,00.05 from the mean value determined by the preparation of model samples or from the value determined by an independent bromatometric procedure for authentic samples. Accuracy expressed as standard deviation of one assay is better than + 5% rel. The total analysis time of one sample is approximately 45 minutes. Depending on the size of the chromatographic plate, however, it is possible to apply several samples side by side and to process several plates at the same time in the development bath, thus reducing the analysis time per sample accordingly.

The method of determining free phenol or cresols according to the invention can be used not only in the laboratory, but also in the in-process control and in particular in the operational practice wherever the production, storage and application of these condensation takes place

260 208 products, mainly phenolic resins and amine hardeners for peroxide resins.

Example 1

At the start of the chromatography plate, a 50 µl sample solution of 0.5 wt. in denatured ethanol, leaving 2 cm from one edge of the plate free. At the start of this free edge, 10 µl of the same solution for reference chromatogram is spotted. Develop the entire chromatogram in hexane-ethyl acetate (70/30 v / v) until the face of the mobile phase reaches almost the upper edge of the plate (25 minutes). After the plate has dried, the edge of the plate is cut off and visualized by spraying a mixture (1: 1 v / v) of 1.5% aqueous ferric chloride and potassium ferrocyanide solutions prepared on the same day. A strip corresponding to the position and size of the phenol elution strip is drawn on the remaining part of the plate as compared to the developed chromatogram. gentle stirring (60 rev. min ^- ^) electromagnetic shaker 10 minutes. Pipette 5 ml of the clear extract from the flask, add 0.1 ml of 0.75N ammonium hydroxide and 0.1 ml of a 0.6% aqueous solution of 4-aminoantipyrine and mix. Next, 0.1 ml of a 2% aqueous solution of potassium hexacyanoferrate is added, and after shaking, the absorbance of the purple color is measured in a 10 mm cuvette against a blank at 510 rm on a Spekol spectrophotometer. For the measured absorbance, the concentration of phenol in the sample solution is determined from the calibration dependence and the phenol concentration in the analyzed original sample is calculated using the formula cjc 4 β V c = -ή- · wo = -4i-. 100,

260 208 where C is the concentration of free phenol in the analyzed resin sample (% m / m), c ^ is the concentration of phenol in the sample solution as determined from the calibration dependence (g. Ml ^), Cg is the dissolved sample concentration (g. Ml ^- ^) V is the volume of the sample solution (ml) and M is the sample weight (g).

The calibration dependence is determined in the same manner, but instead of the phenolic resin solution, a phenol solution of known concentration is applied to the chromatographic plate.

Example 2 •

The procedure was as in Example 1 except that hexane-ethyl acetate (45: 55 v / v) was used to develop the chromatogram, making the reference chromatogram visible with a 1% acetone solution of p-nitrobenzenediazonium fluoroborate. The separated phenol elution wall is transferred to a 100 ml beaker after cutting into three portions. After adding 50 ml of water and covering the beaker with a watch glass, the beaker is allowed to stand for 15 minutes with occasional shaking. The color absorbance after reaction with 4-aminoantipyrine is measured at 520 nm against distilled water.

Example 3

At the start of the chromatography plate, a 50 µl sample of the epoxy resin hardener formed by the condensation of o-cresol, formaldehyde and dipropylene triamine dissolved in ethanol (0.5-1 g of hardener in 50 ml ethanol) was applied in a strip by a constriction pipette. The sample is applied so that one

The 260 208 edge of the chromatographic plate remained about 2 cm free edge. At the start of this free edge, 10 µl of the same solution for reference chromatogram is spotted. Develop the entire chromatogram in hexane-ethyl acetate in a 60:40 by volume ratio until the face of the system reaches almost the upper edge of the plate. After venting the eluate, the reference chromatogram is cut and visualized by spraying with a 1.5% aqueous solution of ferric chloride and a 1.5% aqueous solution of potassium ferrocyanide 1: 1 (both solutions may be mixed just prior to spraying). The comparative chromatogram can be sprayed with a slightly moistened detection reagent to speed up the work. Depending on the position of the elution band of o-cresol in the reference chromatogram, the remaining part of the plate is marked with an elution band of o-cresol, which is cut and quantitatively transferred to a 200 ml ground-glass flask into which 125 ml of distilled water was previously pipetted. The O-cresol is extracted from the plates for 20-25 minutes with occasional stirring.

5 ml of a clear solution are then pipetted from the extraction flask, to which 0.1 ml of 0.75 molar ammonium hydroxide, 0.1 ml of a 0.6% aqueous solution of 4-aminoantipyrine are added and after stirring 0.1 ml of 2% aqueous potassium hexacyanoferrate solution. After shaking again, the absorbance of the purple color is measured in a 10 mm cuvette at 500 nm on a Spekol spectrophotometer against a blank. For the measured absorbance, the concentration of o-cresol in the sample solution is determined from the calibration dependence and the concentration of o-cresol in the hardener analyzed is calculated from the weight and volume of the solvent.

The calibration dependence is determined in the same way, but instead of the hardener solution, an o-cresol solution of known concentration is applied to the chromatographic plate.

Example 4

The procedure was as in Example 3 except that the hardener of the epoxy resins formed by the condensation of tricresol (technical mixtures of o-cresol, m-kre260 208 sol and p-cresol), formaldehyde and diethylenetriamine was subjected to analysis.

For extraction into water, a strip containing all three cresol spots is cut off and the sum of these tresresols is determined from the spectrophotometric determination.

The calibration is again carried out in the same manner as in Example 3 except that tricresol solutions of known concentration are applied instead of a solution of o-cresol of known concentration.

Claims (2)

1. Method for the determination of free phenol or cresols in the condensation products of these compounds with aldehydes and optionally polyamines by thin layer chromatography using a mixture of hexane and ethyl acetate as eluent, characterized in that a strip of solution of the evaluated condensation product in organic The solvent and the chromatogram are developed in a mixture consisting of 40 to 90% by volume hexane and 60 to 10% by volume ethyl acetate to separate the phenol or cresols from the other components, then part of the plate containing these separated compounds is separated, extracted with water and phenol or cresols. contained in the aqueous extract is determined spectrophotometrically. 2. A method according to claim 1, wherein the position of the strip of separated compounds on the plate is determined from a comparative chromatogram that develops on the same plate under the same conditions, then separated and subjected to reagent detection for phenolic substances.