1211
V O L U M E 2 5 , NO. 8, A U G U S T 1 9 5 3 ACKNOW L WGMEKT
Table XI.
Determination of 4llethrin in Cltrasene Allethrin .~ -. - Content, "0 by Wt. ~
Sample Spthetic Ia Synthetic 11" Ka allcthrin in Ultraseiie.
a
Calcd. n 55 0 9i
Found 0.55 0.96
further condensation of the allylniethylcyclopentadienone and its dimer with the excess diamine to form nitrogenous condensation products is to be expected. Application to Determination of Allethrin in Insecticidal Formulations. Some n.ork was conducted on the applicability of the ethylenediamine procedure to the determination of allethrin in insecticidal formulations. Synthetic samples of IC3 allethrin were prepared in Ultrasene (a kerosene fraction) and analyzed by the established procedure, except that a 25-ml. sample was used and at the end of the reaction sufficient pyridine (about 75 ml.) was added to make the solution homogeneoi~s. The results are shoxn in Table XI. I n the examination of any formulation, interference from any other insecticides or synergists which react with ethylenediamine to form a titratable acid must be considered. D D T reacts quantitatively mole for mole with ethylenediamine in 2 to 3 hours at room tempernture. At 98" C., bhe reaction is slightly more than molar. I t is probable that the reaction products of DDT anti ethylenetliamiiie are ethylenediamine hydrochloride and R secondary imine formed by interaction of the primary amine and one of the chlorine atoms in DDT. The amine hydrochloride is titratable with qodiuni methylate in pyridine medium. whereas tlic ermiclar\- a n i i n ~is not.
The authors g~atefullyacknowledge the assi~tanceof the personnel of the various laboratories of Carbide and Carbon Chemicals Co., especially E. F. Hillenbrand, Jr., G. I-. Funk and H. E. Persinger of the Methods Development Group, H R. Guest and his associates of the Research and Development Department, and R. H. Kellman and associates of the Biological Research Group. The authors also are indebted to all of the cooperating members of the C.S.M.A. Chemical Analysis Committee, especially to R. C. Haring, forme] conmiittee chairnian, and to the rhemistq nE the 01 dphaStandard Oil C o of Indiana n ho sugge-terl the naphtholb~nwinintlirator. LITERATURE CITED
La Forge, I-. H.. and Avree, Fled, J r . , Sonl, Sojr;t. ( . ' I , , i ~ ~ i c n k , 17, 95-8, 115 ;.January 1941). La Forge, 1:. B., G r e e n . N a t h a n , and S c h e c h t e ~ .AI. - , , .J. .lm. C'heii?. Soc., 74, 5392 (1952). l l i t c h e l l , W.! and Tresadern, F. fI., .J. SOC.( ' h e m . I d L G l i t l O i l ) , 68, 221 (1949). l l i t c h e l l , IT., Trezwlei n. F. 11.. ani1 W i d , ,accurate, and precise methods of analysis iwornes incwasingly apparent. Of primary importance in the examination of these compounds is the quantitative clt~trrminationof the amounts of ure:t antl formaldehyde present. Owing to tht. inherent nature of tlic rondensatioil renctiori and the loss of formaldehyde through volatilization. determinatioii of the iwpective amounti; of reactantq originally combined is prohibited. However, t'he determination of the mole ratio of urea t o formaldehyde provides a characteristic for n particular resin which is of fundamental importance in research antl rontrol. Coupled with additional physical and c-hemical 1
Present nddresr. Aeroi-ox Corp., S e w Bedford, IIass.
minimum of 99.85'~. The urea anallsis results i n an estimated precision of 3 parts per thousand niaximum de*iation and a recovery of 100 i 0 . 1 7 ~(accuracj). The recovery of urea in fully cured resins varies between 90 and 99%. The method provides a tool for the complete depolymerization of ureaformaldehj de condensates. 4 direct analysis of the major constituents is possible. The method nlay give further impetus to the structural study of ureaformaldehyde condensates and prove to be of value in production control and competitive product analysis.
data, it provides a wluable insight iiito the nature of the rondensation product. Although the urea-formaldehyde mole ratio is nientioneJ frequently in the literature, few procedures are provided which can he utilized satisfactorily by the analy*t in possession of only limited inforniation concerning the nature of the product to be analyzed. Walter (12) states that the hydrolysis of urea clerivatives attained by heating the compound with magnesium chloride (MgCI~.GH?O)in the presence of concentrated hydrochloric acid converts methylene and methylol groups to formaldehyde, the nitrogen to ammonia, and the carbon of the C-0 groups to carbon dioxide. Although no specific analyt,ical procedures are provided, the basic theory of re5in analy.sis i. sum-
,
1212
ANALYTICAL CHEMISTRY
marized. Kittel ( 4 ) reports that urea-formaldehyde resins can be hydrolyzed in hydrochloric acid (specific gravity 1.12 to 1.19) and the liberated formaldehyde can be determined by precipitation with dimedone (l,l-dimethyl-3,5-diketocyclohexane)from a slightly acidic solution. -4lthough Yoe and Reid (IS) have reported the optimum conditions for carrying out this gravimetric procedure, an error of 2% is reported in the analysis of an aqueous formaldehyde solution. Such a discrepancy would not meet the degree of precision necessary in a suitable urea-formaldehyde mole ratio determination.
ever, many solid, unfilled resins vere encountered which made necessary the collection of 350 ml. of distillate for complete formaldehyde recovery. In addition, the method is obviously unsuited for resins which contain volatile acids. Kappelmeier ( 9 , s )has presented a method for the quantitative determination of urea in urea-formaldehyde resins by the action of benzylamine. This reagent converts the urea present in the resin to the dibenzylurea derivative. -4lthough considerable research was necessary to render the method applicable to both liquid and solid resins, the work of Kappelmeier served as the basis for the urea determination procedure described here. GENERAL OUTLINE O F METHOD
In the proposed method the complete depolymerization of urea-formaldehyde resins in all stages of condensation is attained and the amounts of urea and formaldehyde present are recovered, Since other nitrogen-containing compounds (alkanolamines, ammonium salts, etc.) may be present, the nitrogen content cannot be assumed to be due to urea alone. By analyzing for urea directly this difficulty is avoided. In the absence of such compounds, an excellent check on the accuracy of the results is afforded by comparison of the urea and total nitrogen contents. If the nitrogen is present in excess of that required for the amount of urea recovered, the presence of other nitrogen compounds is indicated. SAMPLING O F R E S I N S
Figure 1. Distillation Apparatus for Determination of Formaldehyde In a urea-formaldehyde resin
Nerad (9) has proposed that urea-formaldehyde resins be hydrolyzed in 1 N sulfuric acid n-ith the subsequent removal of liberated formaldehyde by steam distillation. The formaldehyde content of the aqueous distillate is then determined. Attempts to duplicate this method revealed that the aqueous formaldehyde distillate is not sufficiently stable, with the result that formaldehyde is lost through volatilization during the steam distillation. The method of Coppa-Zuccari ( I ) specifies that resin samples be decomposed in an alkaline peroxide solution followed by the steam distillation of the formic acid thus formed. Since no analytical data indicating the precision or accuracy of the method were presented, the method was evaluated through experimentation. The lack of precision and accuracy subsequently encountered was believed due to the extreme volatility of the formic acid and to loss of formaldehyde as methanol as a result of a Cannizzaro reaction. The method employed by Levenson (8) in the study of butanolmodified urea-formaldehyde resins included the hydrolysis of resin samples in a 1 to 1 phosphoric acid solution. The liberated formaldehyde was distilled into a standard alkaline peroxide solution. The formic acid formed by the oxidation of the formaldehyde was determined by titration of unconsumed alkali. This procedure employed a convenient and efficient hydrolyzing agent in addition to a medium in which the liberated formaldehyde could be bound chemically. Both of these features were deemed indispensable in an acceptable method for urea-formaldehyde resin analysis. The precision attained by Levenson was suitable for obtaining relative values, but was not of the degree deemed necessary in an objective analysis. After a thorough evaluation of this method, the precision could not be improved upon and the method was no longer investigated. Levenson stipulated that 150 to 200 ml. of distillate be collected. How-
Proper sampling presents one of the principal problems of ureaformaldehyde resin analysis. Liquid resins present the greater problem om-ing to the varying amounts of unreacted formaldehyde present. For this reason it is recommended that resins be analyzed immediately following withdrawal of the sample from the storage tank or container and that the analysis be performed as soon after manufacture as is possible. If the storage is necessary it should be in airtight containers a t 10" C. Thorough mixing of liquid resins is essential and best results are obtained when small representative samples are introduced into dropping bottles. The sample can then be introduced directly into the reaction flask and weighed by difference. Solid resins are mixed thoroughly prior to analysis. Weighing can be accomplished by any convenient method since loss of sample through volatilization is negligible. DETERMINATION O F FORMALDEHYDE
Phosphoric acid is an excellent agent for the hydrolysis of ureaformaldehyde resins. This acid has the advantage of a relatively low heat of dilution, and complete resistance to entrainment during distillation. The hydrolysis and distillation are carried out in an apparatus having the characteristics of that shown in Figure 1. The liberated formaldehyde is collected in an excess of alkaline potassium cyanide solution in which it is bound chemically as formaldehyde cyanohydrin. HCHO KCN +HzCHOCN KOH KCN (excess) Collection is made directly in a 500-ml. volumetric flask. Originally the distillate was analyzed volumetrically. 4 known excess of standard silver nitrate was added to the cyanide distillate and the unreacted portion was determined by titration with standard ammonium thiocyanate.
+
+
+
Although the above procedure produced results of satisfactory precision and accuracy, the method was too time-consuming and required an analyst experienced in the detection of the end point. Precision and accuracy were improved when the titration was carried out potentiometrically using a silver-silver thiocyanate and platinum electrode system. The analysis was even further simplified when it was found that the silver cyanide precipitate could be collected, dried, and weighed quantitatively. This new principle of analyzing formaldehyde was evaluated by employing it in conjunction with other prominent methods in the analysis of an aqueous formaldehyde solution. The agreement
V O L U M E 2 5 , NO. 8, A U G U S T 1 9 5 3 Table I.
1213
Analysis of Formaldehyde-Water Solution
(Showing agreement of gravimetric cyanide method with other accepted methods) Formaldehyde Recovered, Gram Detn. GraviSodium Hydroxyl Hydrogen Nummetric Volumetric bisulfite amine-HC1 peroxide ber Cyanide cyanide (6) ( 7) (6) 1 0,01794 0.01796 0.01795 0.01792 0.01796 2 0,01795 0.01796 0.01795 0.01795 0,01799 3 0.01795 0.01798 0.01796 0.01798 0,01799
between the results obtained proved the method to be coniparable with generally accepted methods for the analysis of dilute formaldehyde solutions (Table I). Reagents. All reagents are C.P. Phosphoric acid solution. Mix 85% phosphoric acid with an equal volume of distilled water. Potassium cyanide solution. Dissolve 24.8 grams of potassium cyanide and 10 grams of potassium hydroxide in water and dilute to 1 liter. Porous tile chips. Boil porous tile chips in a 20y0 phosphoric acid solution and wash with distilled water. Silver nitrate solution. Dissolve 10.2 grams of silver nitrate in 300 ml. o! water. Nitric acid solution Mix concentrated nitric acid with an equal volume of water. Procedure. Assemble the apparatus. Pipet into a 500-in]. volumetric flask 50 ml. of the cyanide solution. Insert the delivery tube into the flask RO that the tip is well below the surface of the liquid. Place two porous tile chips in the distillation flask. Introduce 0.5 gram of sample (based on the solid content of the resin) into the distillation flask and quickly close the system. Introduce into the dropping funnel 50 ml. of phosphoric acid solution. Allow the solution t o run into the flask in a dropwise manner. Adjust the temperature and water flow from the dropping funnel so that the temperature is maintained a t 110' C. and the system delivers 65 to 70 drops per minute. Collect the distillatr until the volumetric flask contains a total volume of 450 ml. The distillation should take a t least 2 hours. Disconnect the apparatus and wash down the condenser and delivery tube with distilled water. Dilute the distillate to the 500-ml. mark. Introduce into a 250-ml. beaker 25 ml. of the silver nitrate solution and acidify with 2 ml. of nitric acid solution. While stirring, pipette into this solution 100 ml. of the distillate. Allow the precipitate to digest until the supernatant liquid is clear. This may be hastened by mechanical stirring. Collect the silver cyanide precipitate in a previously dried (105" C.) and weighed Gooch crucible. Wash the precipitate by decantation until the washings are free from silver. Dry the crucible and contents to constant weight a t 105' C. Prepare a blank by pipetting 50 ml. of cyanide solution into a 500-ml. volumetric flask and diluting to the mark. Treat the blank in the same manner as the samvle. (TVb - WS) x 112.1 Calculation. Per cent formaldehyde =
the instability of the aqueous formaldehyde solution. This fact was shown by the results obtained from the analysis of previously standardized aqueous formaldehyde solutions. The distillation of the solution was carried out using both aqueous and cyanide collection media. The results summarized in Table I1 show the greater recovery resulting from the collection in the cyanide medium. The quantitative recovery of formaldehyde from a urea-formaldehyde condensate was shown by the analysis of a resin which was prepared in a closed distillation system. The urea (excess) and formaldehyde were introduced into the distillation flask (Figure 1) and the system was immediately closed. -4condensation catalyst was then added through the dropping funnel. Heating was started and the mixture was caused to reflux by directing a stream of air a t the neck of the distillation flask. When the mixture appeared sufficiently viscous to indicate that condensation had occurred, the condensation was cooled and analyzed for formaldehyde content. In this manner the formaldehyde which is ordinarily lost through volatilization during condensation was retained in the cyanide collection medium. The recovery is shown in Table 111.
T a b l e 11. Formaldehyde Recovery Distillates HCHO present, gram HCHO recovered, gram HCHO lost, gram HCHO lost, %
I 0.2625 0.2548 0.0077 2.93
Water Collection I I11 0.2100 0.1575 0.2030 0.1504 0.0070 0.0071 3.33 4.50
IV 0.1050 0.0973 0.0077 7.40
HCHO present, gram HCHO recovered gram HCHO lost r a d HCHO lost: %,
0.2625 0.2624 0~0001 0.04
Cyanide Collection 0.2100 0.1575 0.2099 0.1575 0.0001 0.0000 0.05 0.00
0,1050 0.1050 0.0000 0.00
Table 111. Formaldehyde Recovery f r o m Urea-Formaldeh y d e Resin of K n o w n Composition Detefmination Number 1 2 3
HCHO Added, Gram 0.2625 0.1575 0.2100
HCHO Recovered, Gram 0.2620 0.1574 0.2097
HCHO Recovered,
76 99.81 99.94 99,86
The high degree of precision obtained by this method is shown by the results which are summarized in Table IV. Samples of a liquid anda solid resin were analyzed by two separate operators and the determinations, in triplicate, were performed on different days. Each operator carried through the complete formaldehyde determination, including the sampling of the resins.
s
Wb = weight of silver cyanide in blank Ws = weight of silver cyanide in sample S = weight of sample Interfering Substances., Halogen compounds are the most frequently encountered interfering substances. If the preliminary qualitative examination of the resin reveals the presence of a halogen, the amount present in the formaldehyde distillate must be determined. This is most conveniently accomplished by the method of Polstorff and RIeyer (IO). An aliquot portion of the distillate is withdrawn and treated with an excess of formaldehyde. In this manner the unreacted potassium cyanide is converted to formaldehyde cyanohydrin which will not interfere with the volumetric Volhard method for the determination of halogen. Hydrazine compounds are also known to interfere. This method is also applicable for the determination of total formaldehyde in pure melamine-formaldehyde condensates. Precision and Accuracy. Experiments revealed that the liberated formaldehyde must be collected in a medium in which it is chemically bound. Collection in an aqueous medium results in incomplete retention of the liberated formaldehyde owing to
Table IV. Analyst A
B
D e t e r m i n a t i o n of Formaldehyde i n a Liquid and a Solid Resin Formaldehyde Recovered, % Liquid resin Solid resin 39.18 51.04 39.24 51.02 39.20 51.08 39.20 51.08 39.22 51.06 39.17 51,lO 39.23 51.10 51.04 39.16 51.05 39.19 51.07 39,20 39.23 51.09 39.17 51.06
DETERMINATION OF UREA
The determination is based on the quantitative reaction between urea and benzylamine. The reaction is described by Kappelmeier ( 2 , 3) as the aminolysis of urea-formaldehyde resins in which the products are benzylurea and others which the author
1214
ANALYTICAL CHEMISTRY
did not identify. The reaction is schenutizetl by the following formula : aminolysis Urea-formaldeh\-de C6Hj -CH2--?;R? --+ 0 2( CGHs-CH,--SH,)
+
H!S-I--sH? t CGH~-CH~--TH--C--S€T--CH~-C~H~
+ NH,
The authors are of the opinion that the reactiou involves the coordination of the free electrons of the nitrogen of benzylamine with the electropositive carbon a t o m of the carbonyl groups of the condensate. This is followed by rearrangements and the splitting of ammonia and formaldehyde from the molecule. The dibenzylurea is highly insoluble in acidic medium and separates readily from the I paction mixture with the addition of excess acid. Reagents. Benzylamine (Ihstman Kodak). Hydrochloric acid solution. M i y 1 volume of concentrated acid with 3 volumes of water. Congo red paper. Procedure. Weigh into a 125-ml. iodine flask 0.5 gram of sample based on the solid content. Solid resins should be in the form of a fine powder. Add 15 ml. of benzylamine. Provide an interjoint side arm adaptor with a thermometer for measuring the temperature of the distillate. Assemble the apparatus, plare the flask into a sand bath, and connect the side arm to a suitable manifold for the disposal of fumes and distillate. Apply heat until a water-benzylamine mixture is observed to distill. The temperature will rise to some point below 100’ C. The mixture should distill a t or below this temperature as long as moisture is present in the sample, Should the temperature of the distillate rise above 100’ C., reduce the amount of heat applied to the sand bath. The water-free benzylamine (boiling point, 182’ C.) should reflux from the sides of the flask, but should not distill over. Reflux liquid and spray-dried resins for 8 hours and cured resins for 16 hours. Allow the reaction mixture to cool to 40’ C. and, while stirring mechanically, add the hydrochloric acid solution dropwise until the mixture is acid to congo red indicator paper. Place the flask into an ice bath and continue stirrin until any oil which may have formed becomes crystalline. Coflect the crystals in a previously dried (150’ C.) and weighed sintered glass crucible of medium porosity. Wash the crystals with cold water until free from acid. Dry the crucible and contente to constant weight at 105’ C. The melting point of the crystals should be 165’ to 167’ C. If the resin contains a nitrogen-free filler (wood and shell flows), determine the nitrogen content of the residual dibenzylurea-filler mixture. Since dibenzylurea is the only nitrogen-containing compound present, the per cent of nitrogen can be converted to dibenzylurea and the weight present in the residue can be calculated. W X 25.01 Caiculations. Per cent urea in unfilled resina = S W = weight of dibenzylurea S = sample weight Per cent urea in resins containing nitrogen-free filler = n- x w x 2.111
S
-Y = per cent nitrogen in iesidue It’ = weight of residue
d = sample weight Interfering Substances. In order for a compound to ieact with benzylamine, it must contain, in addition to an amino group, a carbonyl or thiocarbonyl group. Compounds containing these groups therefore constitute interfering substances. Although melamine does not fall into this class, it does form an oil of unknown composition. Discussion. The time reqdired for the apparent breakup of urea-formaldehyde resins appears to be directly proportional to their degree of condensation. Heat-cured resins exhibit marlred resistance to the action of benzylamine and the per cent of urea recovered could not be made to agree with the per cent indicated by the total nitrogen content (see Table V). This fact may be due to some structural arrangement inherent in cured resin9 which cannot react with benzylamine. Increase of time of reflux beyond that stipulated did not result in greater yields and oily products were frequently encountered. Temperature is an important factor in the determination. If the water iq not re-
Table v. Determination of Urea in Various Types of UreaFormaldeh).de Resins Urea Recovered, %--_ From content From 4‘: of ~~~~
Froin
Type of Resin Spray-dried. I
total nitrogen
I1 Heat-cured I Heat-cured 11“ Liquid
I I1
at.
dibensyliirea
dibenzylurea
57 4 57.4
57 3
60.8 80.8
60.: GO ,
57.3 5i.4 60.7 60.7
60.3 60.3 49 3‘ 49 :3 31 0 31 0 23.0
2; i 57 .i
57.9
49.1
49.2 49.3
23.0
111
70 i ‘ L 20 7
5i.i
49 1
30 !J 31.0 23.0 23.j! 20. i “0 s
57,s 30 9 31.0
23.0 23.0 20.8 20.8 50 5
Sway-dried I 30 6 , . with shell B o w 50 6 .. 50.6 a Contains triethanolamine for wliich coinlxnsation has been made. This additive may have a definite effect on thta degree of polymerization.
moved from liquid resins, they sliow little sign of bre:rkup after 8 hours of reflux. This is obviously due to the lowering of the reaction temperature. By heating the reein in the presence of excess benzylamine in an apparatus providing limited reflux area, the Tvater is removed and the reaction temperature rises to a teniprrature near the boiling point of pure benzylamine. SC\I\I4RY
-4precise method for the analyeis of formaldehyde in ureaformaldehyde in all stages of condensation has been presented. Practice has shoxn that the method yields values precise to a t least 3 parts per thousand. The determination for urea yields accurate result9 for :ill but fully cured resins. By comparison of the values obtained for urea and total nitrogen, the prc”mce of nitrogen compounds other than urea is indicated and an estimation of the amounts of these compounds can be made. Once the percentages of urea and formaldehyde are known the mole ratio ir calculated from the following formula: 2
x
cc formaldehvde A
5 urea
-
x
-
Then 1: X = urea: formaldehyde ACKYOWLEDGMENT
The authors express their appreciation to the Borden Co., Chemical Division, for permission to present this paper; and to the Aerovox Corp., which made clerical time available to make this publication possible. REFERENCES
Coppa-Zuccari, G., Inds. Plastiques, 4 , 183 (1948). Kappelmeier,C. P. A , P a i n t , Oil,Chem. Reu., 3, Xo. 4, 8 (1948). Itlid., 115,
NO.
2, 1 4 (1952).
Kittel, H., Farben, Lacke, Anstrichstofe, 2, 1 (1948). Kolthoff, I. RI., and Stenger, V. A., “Volumetric *%nalysis,” Vol. 11, p. 219, New York, Interscience Publishing Co.. 1947. Ibid., p. 221. Ibid., p. 222. Levenson, J. J., ISD. ESG.CHEM.,ANLL.ED.,12,332 (1940). Xerad, Z., Chem. Listy, 44, 35 (1950). Polstorff, K., and Meyer, H., 2. a n d . Chem., 5 1 , 6 0 1 (1912) Walker, J. F., “Formaldehyde,” p. 262, New, York, Reinhold
Publishing Corp., 1944. Walter, G., Trans, Faraday Soc., 32, 379 (1936). Toe, J. H., and Reid, L. C., IND.EXG.CHEM,,ANAL.ED., 13,
238 (1941). RECEIVED for review September 19, 1952. Accepted M a y 13, 19.53. Presented before the Division of Paint, Varnish, and Plastim Chemistry a t the 122nd Meeting of the A M ~ R I C ACXx ~ ~ r c SOCIETY, .4~ -4tlantic City. N.J.
