Analyst, February, 1973, Vol. 98, $9. 107-115 107 Thin-layer Chromatography of Simple Urea - Formaldehyde - Methanol Reaction Products Part I.* Qualitative Aspects BY P. R. LUDLAM (The Borden Chemical Company ( U . K.) Limited, North Baddesley, Southampton, SO6 9ZB) Methods are described for the preparation of addition and condensation products of urea and formaldehyde of low relative molecular mass and their methyl esters. The stability of these compounds both as solids and in solution is discussed. Conditions are described that enable most compounds to be separated adequately by thin-layer chromatography without decomposition or other reaction occurring on the plate. The implications of the colours given by the compounds on a chromatographic plate and the effect of sub- stituents on the RF value are discussed.FOR many years resins manufactured by the condensation of urea and formaldehyde under various conditions and over a range of molecular ratios have held a position of considerable importance in the adhesive, textile finishing and moulded plastics fields. Many commercial urea - formaldehyde resins contain only moderate amounts of material with a relative molecular mass of less than 200. Because of the large number and extreme complexity of compounds of high relative molecular mass, this work was mainly directed towards the chromatographic separation of compounds with relative molecular masses below about 200. Methanol is nearly always present in commercial formaldehyde, either in small amounts, as a result of incomplete oxidation during manufacture, or at the 2 to 10 per cent.level, when it is added in order to improve the stability of the solution. If, during the preparation of urea - formaldehyde condensation products the reaction mixture is made even mildly acidic, there will be a tendency for any methanol present to undergo etherification reactions with methylol (hydroxymethyl) groups present. Occasionally substantial amounts of methanol are added to reaction mixtures with the intention of forming ethers and consequently modify- ing the properties of the final resin. Thus, as methyl ethers are to be expected in resins, and for analytical considerations that will be discussed in detail in Part I1 of this paper, the methyl ethers of the methylol compounds have been prepared and studied by thin-layer chromatography.Chromatographic studies of urea - formaldehyde - methanol condensation products of low relative molecular mass have been made by Hamadal and Inoue and Kawai2 on paper in one dimension. The poor separation of urea, monomethylolurea and dimethylolurea severely limits the information that can be obtained on commercial products. It03-5 carried out two-dimensional chromatography on paper with methanol in one direction and pyridine - chloroform - water (17 + 8 + 3) in the second dimension. Good separation was obtained and a careful examination of resinous condensates was undertaken. No reference can be found to chromatography on thin layers or to any quantitative aspects of chromatography in this field. A major consideration in the chemistry and chromatographic separation of urea - formaldehyde - methanol compounds is their instability. In general, they are reactive materials ; they will polymerise, disproportionate or decompose readily.A few important generalisations can be made : (i) Methylenediurea is stable in the solid form. It will, however, hydrolyse in aqueous solution, the reaction being catalysed by hydrogen ionss (ii) The ethers are more stable, both in solution and as solids, than the methylol com- pounds and can be stored for many months at room temperature without marked decom- position. * For Part I1 of this series, see p. 116. 0 SAC and the author.108 LUDLAM : THIN-LAYER CHROMATOGRAPHY OF SIMPLE [ArtabSt, Vol. 98 (iii) The methylol compounds, even if prepared in a pure state and stored at normal temperatures, show indications of decomposition after a few weeks and, in aqueous or alcoholic solution, can show some indication of decomposition or reaction after a few hours.(iv) The reactions of methylol compounds and, to a lesser extent, the ethers, are catalysed strongly by hydrogen ions. Therefore, if their solutions are applied directly to chromato- graphic plates of an acidic nature, decomposition will occur. This problem can be overcome by pre-treating the plates with ammonia vapour immediately before application of the solutions. The simplest compounds that can be formed from urea and formaldehyde under alkaline conditions are monomethylolurea, I, and dimethylolurea, 11. These compounds can easily H2N-CO-NH-CH2-OH HO-CH2-NH-CO-NH-CH2-OH I I1 I11 IV CHa-O-CH2-NH-CO-NH-CH2-OH H2N-CO-NH-CH2-NH-CO-NH2 V VI H2N-CO-NH-CH2-O-CHS CHS-O-CHZ-NH-CO-NH-CH2-O-CH 3 be converted into their methyl ethers, i.e., monomethylolurea monomethyl ether, 111, and dimethylolurea dimethyl ether, IV.Dimethylolurea monomethyl ether, V, can also be prepared. These five simple compounds of urea, formaldehyde and methanol have all been prepared in a chromatographically pure condition. By causing formaldehyde to react with excess of urea under acidic conditions methylenediurea, VI, can be prepared in a pure, crystal- line condition. This last compound, as with urea, will readily condense with formaldehyde and methanol at the primary amido nitrogen atoms, thus giving a series of compounds analogous to that formed by urea.All of these methylol compounds and their ethers have been prepared but all contain contaminants to a lesser or greater extent. However, by comparing their chromatographic behaviour with that of the urea derivatives, an unambiguous identification can be made on the chromatographic plate. If, during the preparation of methylenediurea from urea and formaldehyde, the urea is not present in a large enough excess, considerable contamination of the product with di- methylenetriurea will result. This substance has not been obtained in a pure form but it can be identified on the chromatographic plate. SYNTHESIS OF COMPOUNDS FOR CHROMATOGRAPHY All of the compounds discussed above can be obtained from urea, formaldehyde and methanol according to the processes illustrated in Fig.1. MONOMETHYLOLUREA- The method used for the synthesis of monomethylolurea is essentially that of Einhorn and Hamburger.' However, the preparation is simplified slightly by using disodium hydrogen orthophosphate instead of barium hydroxide to attain the necessary pH. A two-fold excess of urea prevents contamination of the monomethylolurea with dimethylolurea, which, if formed in any significant amount, is extremely difficult to remove by simple recrystallisation procedures. Dissolve 1 g of disodium hydrogen orthophosphate in 42 g of 36 per cent. aqueous form- aldehyde (methanol up to a limit of 10 per cent. in the formaldehyde will not interfere). To the solution add 60 g of urea and stir the mixture while maintaining the temperature at less than 25 "C by running water round the reaction vessel.When the urea has completely dissolved, after about 2 hours, place the reaction vessel and its contents in a refrigerator at a temperature of 0 "C for 15 to 24 hours, by which time the reaction mixture will have solidified. Break up the mass and form a slurry with about 20 ml of industrial methylated spirit containing 1 per cent. V/V of a 10 per cent. m/V aqueous solution of disodium hydrogen orthophosphate, filter and recrystallise twice from ethanol containing disodium hydrogen orthophosphate as before. Thin-layer chromatography (described below) indicates that the monomethylolurea prepared by this method is free from significant amounts of urea and other urea derivatives. The melting-point (capillary method) was found to be 111 "C.The value given in the literature is 111 "C.7(DMU.MME) 9/, (MMU) U.CH2.0.CH3- HO.CH2.U.CHz.O.CH3 (MMU.MME) 109 (DMU) 3 l5 C H 3 .O .C H 2. U . C H 2 .O G H 3 (DMU.DME) DIMETHYLOLUREA- Dimethylolurea is prepared by the customary method.* Dissolve 1 g of disodium hydrogen orthophosphate in 169 g of 36 per cent. aqueous form- aldehyde and add 60 g of urea. Stir the mixture while maintaining the temperature at less than 25 "C by running water round the reaction vessel. When the exothermic reaction has subsided, after 2 hours, place the reaction vessel and contents in a refrigerator at a temperature of 0 "C for 15 to 24 hours. Filter off the crude product and recrystallise twice from industrial methylated spirit. Thin-layer chromatography shows that the dimethylolurea prepared by this method is free from significant amounts of urea and other urea derivatives.An accurate melting-point (capillary method) cannot be obtained as the decomposition of dimethylolurea commences at temperatures below its melting-point. The melting-point as determined on a hot-plate is 136 "C (with decomposition). Values given in the literature range from 126 "C* to 139 OC.Q METHYLENEDIUREA- KadowakilO described a method for the preparation of methylenediurea but, as prepared by his procedure, it was heavily contaminated with dimethylenetriurea, which it was extremely difficult to remove. However, if the molar ratio of urea to formaldehyde is increased from 4: 1 to 10: 1, pure methylenediurea can easily be prepared, albeit in low yields.The con- siderable urea contaminant is removed quantitatively during recrystallisation. Aqueous formaldehyde (44 per cent.) is used in this method for the preparation of methylenediurea as it is essentially free from methanol and therefore the formation of methyl ethers in the reaction mixture is prevented. It is, however, unlikely that the use of formaldehyde containing up to 6 per cent. of methanol would cause undue problems in the purification of the methylene- diurea. Stir 400 g of urea with 300 ml of water, 21 g of 44 per cent. aqueous formaldehyde and 2 g of phosphoric acid until all the urea has dissolved. After leaving it to stand for 24 hours at room temperature, cool the solution to 0 "C and leave it for a further 24 hours. Filter off the crude methylenediurea and recrystallise it twice from water.110 LUDLAM : THIN-LAYER CHROMATOGRAPHY OF SIMPLE [Analyst, VOl.98 Thin-layer chromatography shows that the methylenediurea is free from urea, dimethyl- enetriurea and other urea condensation products. As with dimethylolurea, decomposition begins to occur below the melting-point but the melting-point on a hot-plate was found to be 208 "C. The value given in the literaturelo is 218 "C. MONOMETHYLOLUREA MONOMETHYL ETHER- The method used for the preparation is that described by Kadowaki.lo Add 4-25g of pure monomethylolurea to 25 ml of methanol containing one drop of 5 N hydrochloric acid and shake or stir the mixture vigorously. The monomethylolurea should dissolve and react within 1 minute. Next, add 0.3 g of finely powdered silver carbonate, continuously shaking the flask to ensure complete and rapid neutralisation of the hydrochloric acid.After 5 minutes, filter the solution and remove the methanol at room temperature by evaporation in a jet of air or in a rotary evaporator. Recrystallise the crude ether twice from ethyl acetate. Thin-layer chromatography shows that the ether is free from significant amounts of impurities such as monomethylolurea or dimethylolurea and its ethers. The melting-point by the capillary method was found to be 91 "C. The value given in the literaturelo is also 91 "C. DIMETHYLOLUREA DIMETHYL ETHER- Kadowaki's method for synthesislo is analogous to that used for monomethylolurea monomethyl ether and was found to be suitable. Add 5 g of pure dimethylolurea to 50 ml of methanol containing one drop of 5 N hydro- chloric acid and shake or stir the mixture vigorously.After 1 minute, when dissolution should be complete, add 0.3g of finely powdered silver carbonate and shake or stir the mixture continuously to ensure complete and rapid neutralisation of the hydrochloric acid. After a further 5 minutes filter the solution and remove the methanol at room temperature, either by evaporation in a jet of air or in a rotary evaporator. Recrystallise the crude ether twice from ethyl acetate. Thin-layer chromatography shows that the ether is free from significant amounts of impurities such as monomethylolurea and dimethylolurea. The melting-point, determined by using the capillary method, was 101 "C.The value given in the literaturelo is 101 "C. DIMETHYLOLUREA MONOMETHYL ETHER- Monomethylolurea monomethyl ether was allowed to react with formaldehyde under slightly alkaline conditions to give a pure, crystalline product. Dissolve 0.1 g of disodium hydrogen orthophosphate in 1 ml of water and add 4.2 g of 36 per cent. aqueous formaldehyde and 5.2 g of monomethylolurea monomethyl ether. Shake the mixture to dissolve the solid material and maintain the temperature at less than 25 "C, by use of running water, for 2 hours. Place the reaction mixture in a refrigerator maintained at 0 "C for 24 hours. Filter off the crystals and dissolve them in 15 ml of ethanol, add 50ml of ethyl acetate and set the solution aside to facilitate crystallisation. Finally, recrystallise twice from 90 + 10 ethyl acetate - ethanol to obtain platelet crystals.Thin- layer chromatography shows that impurities are not present in significant amounts. The melting-point, determined by use of the capillary method, was 98 "C. The value given in the literaturell is 94 to 96 "C. METHYLOLMETHYLENEDIUREAS- By analogy with the preparation of monomethylolurea and dimethylolurea, it should be possible to prepare monomethylolmethylenediurea and dimethylolmethylenediurea by reacting methylenediurea at pH 9 with 1 and 2 mol of formaldehyde, respectively. However, the solubilities of methylenediurea and its methylol derivatives in water are low so that dilute solutions have to be used in the initial condensation procedure, which results in relatively poor yields.Similarly, purification procedures are hampered by the solubility characteristics. If methylenediurea and formaldehyde in a molar ratio of 1 : 1 are made to react together at pH 9 for 24 hours a t room temperature the reaction mixture contains not only mono- methylolmethylenediurea and methylenediurea but also a considerable amount of the di- methylol compound. The incidence of the dimethylol compound can be reduced considerably by using less formaldehyde (e.g., a molar ratio of 1:0-73) but it still proves impossible to remove the dimethylol compound by simple crystallisation procedures.February, 19731 UREA - FORMALDEHYDE - METHANOL REACTION PRODUCTS. PART I 111 In the preparation of dimethylolmethylenediurea , if an excess of formaldehyde were used, the concentration of the monomethylol compound would be expected to be small.This proved to be so, but difficulties were again encountered in the purification of the crude reaction mixture, caused by the excess of formaldehyde remaining in solution, presumably as the hemiacetals of the methylol compounds, and causing a marked tendency for poly- merisation reactions to occur. These preparation difficulties have not been overcome but the following procedures do produce fairly stable solids with the desired compound in the greatest concentration. The impurities present are those which are to be expected and can easily be identified on the chromatographic plate. MONOMETHYLOLMETHYLENEDIUREA- Dissolve 1.3 g (0.01 mol) of methylenediurea in 25 ml of hot water containing 0.1 g of disodium hydrogen orthophosphate.Cool the solution quickly and, before the methylene- diurea crystallises out, add 0.61 g (0-0073 mol) of 36 per cent. aqueous formaldehyde. Stir the solution overnight at room temperature and then evaporate it to dryness at a temperature not exceeding 30 "C, either in a rotary evaporator, or by passing a jet of air over the solution in an evaporating basin. The residue will contain dimethylolmethylenediurea as an impurity and also a considerable amount of methylenediurea. The methylenediurea can be removed by dissolving the crude methylol compound in 30 ml of hot 80 + 20 water - ethanol mixture and cooling quickly. The methylenediurea remains in solution and the methylol compounds precipitate out. The ratio of monomethylolmethylenediurea to dimethylolmethylenediurea is not changed by this procedure.DIMETHYLOLMETHYLENEDIUREA- Dissolve 1.3 g (0.01 mol) of methylenediurea in 25 ml of hot water containing 0.1 g of disodium hydrogen orthophosphate. Cool the solution quickly and, before the methylene- diurea crystallises out, add 1.7 g (0.02 mol) of 36 per cent. aqueous formaldehyde. Stir the solu- tion overnight at room temperature and then evaporate it to dryness at a temperature not exceeding 30 "C, either in a rotary evaporator or by passing a jet of air over the solution in an evaporating basin. The solid thus obtained contains some of the monomethylol compound as an impurity and also some unchanged methylenediurea. The latter compound can be removed by dissolving the solid in 30 ml of hot 80 + 20 water - ethanol and cooling quickly.The ratio of monomethylolmethylenediurea to dimethylolmethylenediurea is not effectively altered by this procedure. MONOMETHYLOLMETHYLENEDIUREA MONOMETHYL ETHER- The impure monomethylolmethylenediurea can easily be converted into the methyl ether by the following procedure. Reduce 1 g of monomethylolmethylenediurea to a fine powder and suspend it in 20 ml of methanol. Add 1 drop of concentrated hydrochloric acid and stir the mixture for 3 minutes, by which time most of the impure methylol compound should have reacted and passed into solution. Add 0.3 g of silver carbonate, grinding the particles with a glass rod against the walls of the vessel to ensure rapid and complete neutralisation of the free acid. Stir the solu- tion for 5 minutes and then filter.Evaporate the filtrate to dryness at room temperature in a rotary evaporator, or, alternatively, by passing a jet of air over the surface of the liquid. The remaining solid is mostly monomethylolmethylenediurea monomethyl ether, but contains a considerable amount of dimethylolmethylenediurea dimethyl ether. DIMETHYLOLMETHYLENEDIUREA DIMETHYL ETHER- The reaction of 1 g of crude dimethylolmethylenediurea with methanol is carried out by a procedure exactly analogous to that described above for the monomethylol compound. The solid resulting from the evaporation of the neutralised methanolic solution is mainly dimethylolmethylenediurea dimethyl ether, but contains some monomethylolmethylenediurea monomethyl ether. DIMETHYLOLMETHYLENEDIUREA MONOMETHYL ETHER- This material, so far obtained only in a very impure form, is made by condensing crude monomethylolmethylenediurea monomethyl ether with an equimolar amount of form-112 LUDLAM: THIN-LAYER CHROMATOGRAPHY OF SIMPLE [AfiaZyst, Vol.98 aldehyde in aqueous solution at pH 9.5. The resulting material contains dimethylolmethylene- diurea dimethyl ether, monomethylolmethylenediurea monomethyl ether and methylenediurea as the principal impurities. Dissolve 0.8 g of crude monomethylolmethylenediurea methyl ether in 1 ml of water containing 0.1 g of disodium hydrogen orthophosphate. Add 0.25 g of 36 per cent. aqueous formaldehyde and allow the solution to stand at room temperature overnight. Filter off the crude dimethylolmethylenediurea monomethyl ether.CHROMATOGRAPHIC DETAILS PLATES- Commercial thin-layer plates of several kinds have been used but none seems to offer any significant advantage over Merck Kieselgel F264 (fast running) spread on glass plates. The plates are not activated before use but are stored over silica gel. Immediately before use, the plate is exposed to ammonia vapour for a few seconds by holding it in the chromato- graphic chamber above the solvent, which contains ammonia. ELUTING SOLVENT- Numerous solvent systems have been investigated, and it was found to be generally true that the presence of ammonia, or some other basic compound, is essential for adequate separation, notably of urea, monomethylolurea and dimethylolurea, to be achieved. Two solvent systems have proved to be satisfactory: ethyl acetate - methanol - ammonia solution (sp.gr. 0.880) (88 + 6 + 6) is used when the emphasis is on the separation and detection of ethers and methylol compounds of urea; and ethyl acetate - methanol - ammonia solution (sp. gr. 0.880) (80 + 15 + 5) when examining mixtures for methylenediurea, the methylol- methylenediureas and dimethylenetriurea. CHROMATOGRAPHIC TANK- ensure that the atmosphere in the tank was saturated with solvent. DETECTION PROCEDURES- Many spray reagents and detection procedures have been examined in the course of this investigation. Some, such as picric acid, ninhydrin, Schiff’s reagent, phenylhydrazine - nickel sulphate, potassium permanganate in dilute sulphuric acid and various concentrations of potassium dichromate in sulphuric acid, were found to be either very insensitive or very specific, e.g., Schiff’s reagent gave colours only with compounds that liberated formaldehyde.Some procedures were partially successful and were used for a time, often until a more suitable method was found. These reagents and procedures include the following. p-Dimethylaminobenzaldehyde in ethanol, 1 per cent. solution-The plate was sprayed with the reagent and placed for 5 minutes in a vessel saturated with hydrogen chloride. This reagent showed good sensitivity to urea and compounds containing primary amido groups but secondary amido compounds were detected only at relatively high concentrations. The contrast between the spots and the background plate (yellow on white) was poor. Dichloropuoresceinn solution - bromine vapour-The plate was slightly moistened by spray- ing it with 0.05 per cent. dichlorofluorescein in 1 N sodium hydroxide solution, exposed to bromine vapour until the initial pink colour was discharged and finally sprayed heavily with the dichlorofluorescein solution.Pink spots were produced on a pale yellow background. This procedure was sensitive but the factors that are involved in colour formation were not easily controlled and reproducibility was found to be poor. Any ammonia or basic materials remaining on the plate also interfered with colour production. The sensitivity was found found to be about 0.2 pg for dimethylolurea. Alkaline potassium pentacyanonitrosylfe rrate(III) (potassium nitroprusside) - potassium hexacyano ferrate(III) solution-Equal volumes of 10 per cent.solutions of potassium penta- cyanonitrosylferrate(III), potassium hydroxide and potassium hexacyanoferrate(II1) were mixed and used immediately, as the mixture is stable for only about half an hour. Purple spots were produced on a brownish yellow background. Two main drawbacks were found with this spray: it was fairly insensitive, as the minimum amount of dimethylolurea that Both solvents must be prepared daily. The tank used in this work measured 22 x 22 x 7 cm. No precautions were taken toFebruary, 19731 UREA - FORMALDEHYDE - METHANOL REACTION PRODUCTS. PART I 113 could be detected was 15 pg; and the colours faded within 5 minutes, making it necessary to photograph the plates in order to allow full interpretation.ADOPTED PROCEDURE- The most widely suitable procedure consists in exposing the plate to chlorine gas and, after allowing sufficient time for the excess of chlorine to disperse, spraying the plate with a solution of an aromatic amine in glacial acetic acid. Of the aromatic amines tested, o-dianisidine is probably the most sensitive, but compared with o-toluidine, which is the amine preferred in this work, it has several disadvantages: the colours of the spots are not so informative as those produced by o-toluidine; even after allowing the chlorine to disperse for several hours, a strong and variable background colour is produced; the storage life of the plate is only a few days a t most, whereas plates sprayed with o-toluidine can be stored for several weeks; and the toxicity of o-dianisidine is probably much greater.SPRAY REAGENT- The spray reagent chosen was a 5 per cent. solution of o-toluidine in glacial acetic acid. The solution is stable for up to 8 weeks, after which the colours of the spots produced by the reagent become less reliable. The chlorine - o-toluidine procedure is capable of detecting approximately 1 pg of sub- stances that give blue spots (urea, methylenediurea, etc.), 3 pg of substances that give green spots (monomethylolurea, etc.) and 5 pg of substances that give yellow spots (dimethylol- urea, etc.). METHOD Prepare 5 per cent. solutions of the reference compounds in methanol when possible. Methylenediurea and its methylol derivatives are almost insoluble in methanol and aqueous solutions should be prepared, by heating to 70 "C if necessary. The hot, aqueous solutions should be spotted on to the plate as quickly as possible so as to prevent excessive reaction.Urea - formaldehyde reaction mixtures are best applied to the plate as solutions of up to 20 per cent. concentration in 1 + 1 methanol - water. Spot 1 pl of each solution on to the ammonia-treated pIate, allow the spots to dry and develop the chromatogram in the solvent mixture of the appropriate proportions for the requirements (see Eluting solvent). Allow the plate to dry at room temperature for 15 minutes after development. (Elevated drying temperatures can cause decomposition of the compounds to take place on the plate, leading to reduced spot intensities and unexpected spot colours.) Next, expose the dry plate to chlorine gas, either in a separate vessel or by directing the gas from a cylinder on to the plate in a fume hood. The uptake of chlorine is rapid and complete chlorination is achieved in a few seconds.Allow the excess of chlorine to disperse from the plate for 5 minutes at room temperature and then spray the plate with the 5 per cent. o-toluidine in acetic acid solution. A preliminary examination of the plate can be made after a few minutes but the full colours take about 8 hours to develop. It is recommended that during this time the plate be kept in the dark. Plates thus prepared are stable for several weeks. RESULTS AND DISCUSSION Idealised separation patterns and R, values of the compounds are shown in Fig. 2. Although a specific method for the preparation of dimethylenetriurea is not given, it can be observed in crude methylenediurea prepared with a molar ratio of urea to formaldehyde of 6: 1 or less, and for this reason its position on the chromatographic plate is shown.Form- aldehyde is often present with the urea derivatives and is chromatographed as hexamine, owing to reaction with the ammonia in the solvent system. The colours given by the various urea derivatives are characteristic of the chemical groupings in the molecule or, to be more specific, the degree of substitution on the amido nitrogen atoms. The primary amido grouping -CO.NH, produces a blue colour, while substituted amido groups, - C O . N H R , where R is either -CH,OH or -CH2.0CH8, give a yellow colour. Thus urea, methylenediurea and dimethylenetriurea give blue spots, while dimethylol compounds and their ethers give yellow spots.The monomethylol derivatives of urea and methylenediurea, together with their ethers, contain one grouping that is associated with a blue114 LUDLAM : THIN-LAYER CHROMATOGRAPHY OF SIMPLE [AfidySi!, VOl. 98 colour and one that is associated with a yellow colour. As would be expected, these compounds give green spots. It is of interest to consider also the effect of the various chemical groupings on the RF values of the parent compound. For both the series based on urea and that based on methylenediurea, the replacement of an amido hydrogen with a methylol group, -CH,.OH, lowers the RF value, while replacement with a methoxymethyl group, -CH,.OCH,, increases the R, value.This relationship is illustrated in Fig. 3 for one solvent system. It has been previously stated that the solvent should be prepared daily. However, during the course of a working day, changes do occur in the solvent system, probably because of the formation of acetamide from the ethyl acetate and ammonia. The only compound that is markedly affected by this solvent change is hexamine (from formaldehyde), which progressively moves to a lower RF value. This shift can be advantageous on occasions, such as when a small amount of urea is to be detected in the presence of a large amount of form- aldehyde. If the chromatogram is run in solvent that is approximately 4 hours old, satis- factory separation can be achieved. Solvent front 0 1 2@ 0 3 40 :::la @5.6 03 0 4 0.4 5 0 010 0.5 110@12 0.3 Fig.2. Positions of the products of the reaction of urea, formaldehyde and methanol on a silica gel plate. Solvent systems: (a), ethyl acetate - methanol - ammonia solution (80 + 16 + 6); and ( b ) , ethyl acetate - methanol - ammonia solution (88 + 6 + 6). The spots are identified following the system used in Fig. 1 : 1 = DMU.DME; 2 = MMU.MME; 3 = DM.MDU.DME; 4 = DMU.MME; 6 = MM.MDU.MME; 6 = urea; 7 = formaldehyde; 8 = DM.MDU.MME; 9 = MMU; 10 = MDU; 11 = DMU; 12 = MM.MDU; 13 = DM.MDU; 14 = DMTU; and a and b are unknown compounds. Colours of spots : open circles, yellow ; closed circles, blue ; and half-closed circles, green During the chromatographic separation of the urea derivatives described in this paper and of other urea condensation mixtures, only two minor spots [(a), yellow and (b), green (see Fig. Z)] have been observed that have not so far been identified.The study of commercial urea - formaldehyde compositions by this method is limited. Because of the multitude of compounds of medium and high relative molecular mass present in these materials, the region of the chromatogram below urea tends to form a streak. This fact, coupled with the coincidence of monomethylolurea and methylenediurea when using both solvent systems, makes the quantitative or semi-quantitative determination of mono- methylolurea and dimethylolurea difficult. The determination of these simple compounds of low relative molecular mass is described in Part 11.February, 19731 UREA - FORMALDEHYDE - METHANOL REACTION PRODUCTS. PART I 115 DMU.DME ! 0-8 1 DM.MDU 4 L Increasing rnethylol Increasing ether substitution substitution Fig. 3. Effect of amido substitu- tion on RB values. Solvent system: ethyl acetate - methanol - ammonia solution (88 + 6 + 6). The compounds are identified following the system used in Fig. 1 I thank Mr. P. Lewis for his interest in the work, his translation of the Japanese papers and for reading the manuscript. 1. 2. 3. 4. 6. 6. 7. 8. 9. 10. 11. REFERENCES Hamada, M., J . Chem. SOC. Japan, Ind. Chem. Sect., 1965, 58, 286. Inoue, M., and Kawai, M., “Research Report of the Nagoya Municipal Industrial Research Insti- Ito, Y.. J . Chem. SOC. Jaflan, Ind. Chem. Sect., 1969, 62, 1918. De Jong, J. I., and De Jonge, J., Recl Trav. Chim. Pays-Bas Belg., 1963, 72, 202. Einhorn, A., and Hamburger, A., B e y . dt. chem. Ges., 1908, 41, 24. Walker, J. F., “Formaldehyde,” Third Edition, Reinhold Publishing Corporation, New York, Sally, J. D., and Gray, J. B., J . Amer. Chem. SOC., 1948, 70, 2660. Kadowaki, H., Bull. Chem. SOC. Japan, 1936, 11, 248. U.S. Patent 2,247,419, 1928. tute,” 1957, No. 17, pp. 1-6. -, Ibid., 1961, 64, 382. -, Ibid., 1961, 64, 386. 1964, p. 379. Received June 21st, 1972 Accepted October 6th, 1972