Alkyl and Substituted alkyl 2-Cyanoacrylates

 .....»-wmwt,......,..,, ..-.~.,..,.,.. ., ‘: W. ‘i a ’/ $/ hi" > J. Adhesion Sci. Techno]. Vol. 4, No. 9. pp. 733-7 (1990) O VSP 1990. M ‘ "\~.. Alkyl and substituted alkyl 2-cyanoacrylate . Part 1. Synthesis and properties V. VIJAYALAKSHMI, J. N. R. VANI and N. KRISHNAMURTP’ Organic Coatings and Polymers Division, Indian Institute of Chemical Technology, Hyderabad 500007, India Revised version received 29 May 1990 Abstract—-Twenty-six alkyl, alkenyl, cycloalkyl, and substituted alkyl 2-cyanoacrylates were synthesized in the pure state. The purity was determined by gas-liquid chromatography, and a correla- tion between the log retention time and the number of carbons in the compounds within the hom- ologous series was deduced. Their physical properties such as parachor and molar refraction were determined and the data were fitted to a linear relation to the number of carbons present in the ester within a homologous series of cyanoacrylates. The tensile strengths of the 2-cyanoacrylate bonds between various metal surfaces are also presented. The tensile strength of the adhesive bonds gradually decreased with an increase in the alkyl chain length. beginning from ethyl cyanoacrylate. Keywords: Cyanoacetates; 2-cyanoacrylates; gas—liquid chromatography; parachor; molar refraction; surface tension; tensile strength. 1 . INTRODUCTION A great deal of literature has been published, mostly in the form of patents and a few as reviews [__1_:_Z], in the past three decades on 2-cyanoacrylates, essentially because of their outstanding property of instant adhesion between a wide variety of surfaces. But very few research papers [8—l8] have been published in compari- son with the patents filed during this period and these were mostly on modification of the physical properties by way of compositions and on polymer degradation studies. However, on careful examination of the available literature, there is hardly any information on the physical properties of substituted alkyl 2-cyanoacrylates. Gas—1iquid chromatographic (GLC) analysis of a few alkyl cyanoacrylates was reported earlier [9]. But GLC data, such as the retention times of the substituted alkyl cyanoacrylates, have not been reported so far. in this paper, we report the synthesis of a wide variety of alkyl, branched alkyl, alkenyl, alkoxy ethyl, haloalkyl, cycloalkyl, and arylalkyl 2-cyanoacrylates in good yields. Some of the 2-cyanoacrylates prepared in this work are reported for the first time. Their physical properties, such as parachor and molar refraction, were also determined. The log retention times of the substituted alkyl 2-cyanoacrylates were determined by GLC analysis. These retention times will be useful in identify- ing a cyanoacrylate or its mixtures in an adhesive composition. The parachor and molecular refraction values give an indication of the purity of the monomers. In future ublications, we intend to report detailed spectroscopic methods of an ysts of these 2-cyanoacrylates. ‘To whom correspondence should be addressed. Supplied by The British Library - "The world's knowledge" »/,».,a..,,..,. 734 I/. Vijayalakshmi et al. 2. EXPERIMENTAL 2.1. Synthesis of alkyl cyanoacetates Most of the cyanoacetate esters were synthesized by reacting an alcohol ( 1.0 mol) with cyanoacetic acid (1.2 mol) in the presence of p-toluenesulphonic acid and benzene in an amount equal to the total weight of the reactants. The water of reaction was removed azeotropically using a Dean—Stark trap. The reaction took nearly 6-8 h for completion and in some cases, where haloalcohols were used, nearly 20 h. The reaction product in benzene was then washed with water to remove excess cyanaoacetic acid and dried over anhydrous sodium sulphate. Benzene was stripped and the product was distilled under reduced pressure. Methyl and ethyl cyanoacetates were prepared in a manner different from the procedures reported earlier [19—21], as shown in the following scheme: _ NaOl-l NaCN Cl—CH2—~COOH *—> Cl—CH2--COONa -:-> CN——CH2—COONa \L HCI CN—CH2—C0OCH2—Cl-I3 CN—CH2COOH This method is tedious, especially during the acid treatment of sodium cyano- acetate, owing to the evolution of hydrogen cyanide gas and also because of the subsequent removal of water from liberated cyanoacetic acid which requires large amounts of pure ethanol. The present method consists of the following sequence of reactions: CICHZCOOH Cl—C.i-I2—COOCH2CH_, CNCHZCOOCHZCH3 H3504 1 2 3 Monochloroacetic acid (1) (1.0 mol) was reacted with a large excess of freshly distilled ethanol (10.0 mol) at reflux temperature for 6-8 h using concentrated sulphuric acid (1% of the total reactants) as the catalyst. Excess alcohol was distilled and the ethyl chloroacetate (2) was extracted with ether and washed free of sulphuric acid with water. Ethyl chloroacetate was distilled at 80°C under reduced pressure (20 mmHg). In the second stage, ethyl chloroacetate (0.25 mol), potassium iodide (0.05 mol), and dimethyl sulphoxide (DMSO) (200 ml) were placed in a 500 ml three-neck round-bottom flask fitted with a stirrer and con- denser. The contents were heated to 40°C and fine powder of sodium cyanide (0.24 mol) was added in three equal portions. The reaction was continued for 4 h and the DMSO solution was filtered to remove potassium chloride. The filtrate was extracted with ether and washed with water, taking all the usual precautions, and dried over anhydrous sodium sulphate. The product was then purified by distillation at 92—93°C (10 mm}-lg). The overall yield was 75°/o based on mono- chloroacetic acid. The purity of ethyl chloroacetate and ethyl cyanoacetate (3) was determined by GLC using a 10% Silar 10 Cp column and the following conditions: column temperature 210°C; injection port temperature 250°C; flame ionization detector temperature 300°C; and hydrogen gas flow 28.5 ml/min. The retention times of ethyl chloroacetate and ethyl cyanoacetate were 1.64 and 5.00 min, respectively. Supplied by The British Library - "The world's knowledge" ...,,,.... 4... .. mm .. ..-.a..m...,.....».»n.-.«»-xv.»-1-um‘-.--v-.. -“’= »’*>ww-my-=sv-vrv:-«.... . _. «.».-2:-.-_~s.m-t—~»~w*:'£'7Wn~r~m-w¥ :w.o2 3.=uo.oS. .8 dz _.....< V. ii ....2m.ouno:§.o 2.. we 3.:2.cE .no.m.En. .uu>_._un. .n ......a._. 742 ‘ ‘ "Supplied by The British Library - "The world's knowledge a.¥:..l..H».v.z.....§.%..¥.4av.a.u.»..u. 743 Alkyl and substituted alkyl 2-cyanoacrylates 5.3 2.? B _ 43 2.8 S.:. mm? 38 3.2 3.2 3.3 _m.o~ 3.2 $2; 3.3 3.? 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S ow :. .....~: S. m ....a.. 8.3 3.3. .22 3% 3.2. mm. .. Sam 3.2 3.2 32 wwmm .23.. am. 5 .35. :....m No.3 o.3~ .....a~ cw... . mm. c .b..m 2.8 2.3 .23 E2 2...: ... m ...5§. _aE._oZ .u_aU _u:=on_ .u_mU vcaom A...\_ V Ew_o>» ....=.5:~u ...3m_.¢uao:m>u-N Aiw: :G_uo~.r_.._2 ._N_o—Z ._o£uN._.w...__ v==.__O> .502 ..M_:uU_O—)_ mo .62 _.O=< mo.n..Cunc:a>u-~ 2: we mu_:o._oE _au_.£Ea .¥...>_..oQ .9 o_._a.H "Supplied by The Bri ish Library - "The world's knowledge" 5 .4. 7 A lkyl and substituted alkyl 2-cyanoacrylates 2.3 2.3. 2.? «new 2.2. M53. 8.3 M52. _ _.~.m 3.2 3% 3.3. 3% 3.3 8.2. Sam :5. vm. 3 3% 8.; «won Emu». 2.9. min». 33 a._$ mmmm 33. 2.3 .23. 3.5. 3% qmmm N._ _m 33 can». c.>~v cam». vwwm 33 town _.mo.m 32. 3% 33 ..::m .25 E2 o3§ Id: Sam. 2.3: 2.2. anon. 8.3: flax? .3. 3: ccdm _ $2. moi. 2.: 0: me. at a2 3: 3. 3: mm. mm. .2 R. 3. f\ 5. l\ (\£tl\ _>.~:om _b< _.cB:o_..iU _b:omo_u>U o_o>U _>..._oEn:o_._U-m __£.88__6-~ 251 :Ec.E-~-mxcEoE :33 58:5 35» axcfim =33 b8_=o2 a.e__< _>w=Eo.£ _.¢c._U _..__< _.€3=< Supplied by The Bri ish Library - "The world's knowledge" + A’/W . __._,...__. 2 :n_._#.._ ~ ~ —————~———-——— - 1 O J L/(ii 1,. _._ O .2 /1 0 746 /i U’ 3 V. Vzjayalakshmi et al. Table 7. Setting times and tensile strengths of 2-cyanoacrylate bonds between metal surfaces Tensile strength (MPa) "*1 MS—MS SS—SS Cu-Cu Alkyl 2-cyanoacrylates Setting time (s) Normal Methyl 0 27.30 15.20 8.80 6.00 5.30 I Ethyl gr 30.30 """19.70 ». 9.20 3' 6.00‘ 5;‘ 5.30 Propyl 5- 1 0 10.12 1 1.56 8.90 5.80 5.00 = Butyl 9.90 11.01 8.30 5.80 5.00 Pentyl 9.62 10.52 7.83 5.60 4.20 7 Hcxyl 9.10 10.21 7.50 5.50 4.20 Heptyl 10-30 8.74 9.90 7.00 5.42 4.50 ; Oclyl 8.21 9.25 6.21 5.31 4.09 1 Branched 5') iso-Propyl .3 22.60 +1. 27.10 «-15.90 18.20 an 19.70 - iso-Butyl 5_1 () 10.12 14.53 12.15 8.97 9.50 sec-Butyl .... 21.26 20.50 18.80 13.90 -E 18.23 .~. iso-Pentyl 14.05 1 1.01 7.83 3.59 7.07 ; 2-Octyl : .m_40 3.20 3.20 2.60 2.20 2.80 2-Ethylhexyl 5 ‘ 4.30 4.52 3.20 3.80 3.40 ==> Alkenyl Allyl ’ 20.36 .. 25.45 ..»l6.20 ‘-17.50 V 16.60 3* Crotyl 5-10 12.40 1 1.90 7.80 7.20 6.80 ~ Propargyl .. 13.90 .. 19.20 4 15.50 _ 16.90 - 14.20 3‘ iv Alkoxy Methoxy ethyl ; H0 .. 20.59 - 24.31 .. 10.16 _ 11.78 .—. 13.16 Ethoxy ethyl = ‘ 15.20 14.39 8.20 9.10 10.16 Butoxy ethyl I (H 5 10.87 10.87 7.60 7.60 9.20 Methoxy-2-propyl ‘ 14.05 1 1.01 6.90 7.60 6.07 Halo 2—Chlor0ethyl S 10.35 10.87 7.03 6.93 7.03 3-Chloropropyl ’ 10.20 10.20 6.93 5.80 6.50 "'i> Cyclo Cyclopcntyl W20 11.59 11.21 4.04 5.94 5.18 Cyclohexyl 6.31 7.45 4.41 5.31 6.18 Aryl Bcnzyl 5 4.41 4.79 3.50 4.03 3.80 MS = mild steel; SS = stainless steel; A1= aluminium; Cu = copper; BR = brass. The experimentally determined parachor and molar refraction of the cyano- acetates and 2-cyanoacrylates showed a high degree of consistency within a hom- ologous series and compared favourably with the theoretical values (Tables 5 and 6). The data are summarized in Figs 2, 3, and 4. The close agreement between the experimentally determined and theoretical values together with the data on purity obtained by GLC are further indications of the purity of the monomers. Expressions of the type y = mx + c for calculations of the parachor, molar refraction. and log retention times of alkyl cyanoacetates and alkyl 2-cyano- ..». V, . ._.... .... Supplied by The British Library - "The world's know|edge"{——-ii‘;-—“T L"’*‘V-“Kai; ::1:.- J...»-lu~».w.....;¢,.i,...,,...m.......¢,.,.A...,,,k.,. .\,‘g,~,,.",_......