CA1043358A - Process for the production of alkene-1,5-diols - Google Patents

Abstract

ABSTRACT OF THE DISCLSURE
PROCESS FOR THE PRODUCTION OF ALKENE-1,5-DIOLS

In the reaction of 3-methy1-3-buten-1-ol with aqueous formaldehyde forming isomeric alkene-1,5-diols, partic-ularly 3-methylene-1,5-pentanediol and 3-methyl-2-pentene-1,5-diols, it has been found that yields of the diols surprisingly are substantially increased if the reaction is effected in the presence of added isobutene.

Description

BA_RGROUND_OF_THE_INENTIION 41 Frel___f_th _Inv__tion 42 This invention relates to a process for the produc- 44 tion of alkene-l,5-diols. More particularly, it relates to a 46 process for the production of a mixture of 3-methylene-1,5- 47 pentanediol and the two geometric 3-methyl-2-pentene-1,5-diol 48 isomers from the reaction of isobutene, formaldehyde and 3- 49 methyl-3-buten-l-ol. 3-methylene-1,5-pentanediol has many uses 50 in organic synthesis and is particularly useful as a precursor 51 for the production of citric acid, as taught in Belgian patents 52 784,238 and 792,076. Also, the alkenediols can readily be 53 hydrogenated .o alkanediols, which are useful in the production 55 of polymers, resins, plasticizers and synthetic lubricants, and 56 as chemical intermediates in the production of materials such 57 as 3-methylvalerolactone. 5a Des_r PtiQn f the P_lor A_t 61 It is known that an alkenol can be reacted with 63 aqueous formaldehyde in the presence of a base to produce 64 alkenediols. More particularly, U.S. Patent 3,692,848 teaches 66 the reaction of 3-methyl-3-buten-l-ol with aqueous formaldehyde 67 at 235 to 400C., thereby forming 3-methyl-2-pentene-1,5-diol. 68 Also, U.S. Patent 2,789,996 discloses the reaction of 70 anhydrous paraformaldehyde with mono-ol such as 3-methyl-3- 71 buten-l-ol to produce the diol 3-methylene-l,5-pentanediol. 72 It is also knovn that al~-3-en-l-ols can be produced 73 by the reaction of isobutene vith aqueous formaldehyde. More 75 particularly, U.S. Patent 3,574,773 teaches the reaction of 76 aqueous formaldehyde with isobutene in the presence of a base, 77 forming 3-methyl-3-buten-l-ol.
Also, U.S. Patent 2,335,027 discloses the reaction of 78 diisobutene with paraformaldehyde to obtain a mono-ol, namely 79 diisobutene carbinol. 80

- 2 - ~ ~

104335~

______________ _ ______ _ In a process for the production of alkene-l,5-diols 85 comprising: 86 (ll contacting in a reaction zone a reaction mixture 88 comprising 3-methyl-3-buten-l-ol and aqueous formaldehyde; 89 (2) reacting said mixture at an elevated temperature 90 and pressure for a period of time sufficient to form said 91 alkenediols, said temperature being below the critical tempera- 92 ture of said reaction mixture, 93 the improvement comprising effecting said reaction in 94 the presence of added isobutene. 95 When sufficient isobutene and formaldehyde are added 96 to the reaction mixture, the process of the invention permits 97 the production of alkenediols vith no net consumption of 3- 98 methyl-3-buten-l-ol, so that the over-all result is production 99 of alkene-l,5-diols from isobutene and aqueous formaldehyde in 100 a single-stage reaction. 101 The exact reasons as to why the process of the 102 present invention is successful in producing the diols in a 103 one-step reaction are not easily pinpointed, although reaction 104 conditions as described herein have been found to give very 105 good yields of the diols. We have noted that added isobutene 108 substantially increases the yield of the diols (i.e., 3-methyl- 109 ene-l,5-pentanediol and 3-methyl-2-pentene-l,5-diols), whereas 111 other olefins in similar systems do not appear to have similar 112 effects. E.g., added isopentene ~2-methyl-2-butene) when 114 making the mono-ol 2,3-dimethylbutene-l-ol and the 115 corresponding diols does not appear to have the same effect as 116 does the added isobutene in making the diols in the process of 117 the present invention. 118 In the process of the present invention, the effluent 120 vithdra~n from the reaction zone, exclusive of isobutene, 121

- 3 -~043358 contains an appreciable amount of the diols, usually at least 2 122 weight percent of the diols, and preferably at least 4-weight 123 percent of the diols. Typically the reaction zone is operated 124 at conditions sufficient to form between about 4 and 40, more 126 usually between about 6 and 20, weight percent of the diols in 127 the effluent withdrawn from the reaction zone, exclusive of ?29 isobutene. The isobutene is excluded from the effluent for 130 purposes of calculating the weight percent diols for c~n- 131 venience, as the isobutene usually readily flashes off from the 133 effluent mixture. Conditions that our data indicate are 134 preferable for achieving relatively high yields of the diols in 135 the effluent include the presence of added isobutene as a 137 centrally important factor; the use of temperatures below the 138 critical temperature of the reaction mixture, preferably a 140 temperature between 150 and 300C., and more preferably 142 between about 180-250C; the maintenance of a pH in the 143 reaction zone between about 4 and 7, preferably by the 144 addition, periodically or continuously, of a buffer comprising 145 a weak polybasic acid and the salt of a weak polybasic acid; 147 and the use of agueous reaction conditions, preferably 148 including the use of agueous formaldehyde. 149 BRIEF_DESCRIPTION _F THE DRAWING 151 FIG. l is a simplified schematic flow diagram of a 153 preferred embodiment of the in~ention, in which the desired 154 alkenediols are produced on a continuous basis. FIG. 2 is a 156 more particular schematic flow diagram of the preferred embodi- 157 ment of the invention illustrated in FIG. l. 158 DEAILED DESCRIPTI_N OF_THE INVENTI_N 160 One mol of isobutene can be reacted with one mol of 162 formaldehyde according to the following eguation: 163

- 4 -~043358 CH3 CT~3 (I)Cll2=C-CH3 + HCHO 2 ~ CH2=c-cl~2-cH2oll 165 (isobutene) ~formalde- (3-methyl-3-hyde) buten-l-ol) A second mol of formaldehyde can be added to the 166 product of I to form isomeric diadducts of isobutene, according 167 to the following equation: 168 (II) CH3 2CH2=C-CH2-Cll2OH + 2HCHO
~CH2-CH201I ~CH2CH20H
CH2= ~ + CH3- ~ 170 (3-methylene-l,5- (3-methyl-2-pentene-pentanediol) 1,5-diols) Surprisingly, when reaction II is carried out in the 171 presence of added isobutene, greatly increased yields cf the 172 diols result. Vie~ed another ~ay, when the two reactions (I 174 and II) are carried out concurrently, yields of the diols are 175 surprisingly higher than if the two reactions were carried out 177 separately. The concurrent reaction of this invention may be 178 represented as follows: 179 (III) CH3 CH3 2CH2=C-CU3 + 4NCIIO + CH2=C-CH2-CII2OH
~Ci~2-CH20~ CH2-CH20H
CH2-C + CH3- ~ + 181 C,H3 CHz=C-CH2-CH2OH

~y higher yields of the diols it is meant that the 182 yields of the diols from the concurrent reactions, based on 183 converted 3-methyl-3-buten-l-ol, isobutene, or formaldehyde, 184 are higher than would be obtained if the reactions ~ere carried 185 out sequentially, as illustrated by equations I and II. 186 ~04335~
Carrying out the reactions concurrently has many 187 other process advantages besides the higher yields of diols. 188 One advantage is the use of 3-methyl-3-buten-l-ol as a solvent 190 to dissolve isobutene, thus facilitating liguid-phase 191 conditions essential in reaction (I~. Starting with a mixture 192 containing 3-methyl-3-buten-l-ol allows the 3-methyl-3-buten-l- 193 ol to act both as a reactant and as a solvent for the 194 isobutene. The 3-methyl-3-buten-l-ol is also a solvent for the 195 agueous formaldehyde, further facilitating liquid-phase 197 contacting of the reactants.
Another important advantage is that the process of 198 the invention allows one to form the desired diols from iso- 199 butene and formaldehyde in a single-stage, continuous process 200 in which make-up isobutene and agueous formaldehyde are fed to 202 a reactor. Crude product from the reactor is separated into 203 various portions, for example an alkenediol product portion and 205 a second portion comprising water, formaldehyde, 3-methyl-3- 206 buten-l-ol and isobutene, which after partial dehydration is 207 recycled to the reactor.
The process of this invention is carried out at a 208 temperature from 150C. to 300C., ~ith 180 to 250C. being 209 preferred. It is important, however that the reaction be 210 carried out with at least part of the reactants in the liguid 211 phase. Thus, the reaction temperature should not exceed the 212 critical temperature of the reaction mixture. The critical 214 te~perature will depend upon the concentration and physical 215 properties of reactants and any solvents present in the 216 reaction mixture. The critical temperature of any mixture can 217 readily be estimated from Kay's rule, R. C. Reid and T. K. 218 Sherwood, "The Properties of Gases and Liguids," Second Ed., 219 1966, using the known physical properties of the pure compo- 220 nents of the mixture. A critical temperature of 132C. was 222 estimated for formaldehyde by comparison with acetaldehyde and 224 from the differences in critical temperatures for various 225 alcohols.
Reaction pressure is not a critical variable, and may 226 vary widely within the scope of the invention. The pressure 228 should be high enough to keep most of the materials in the 229 liguid phase at the reaction temperature. In particular, it 230 should be high enough to keep a substantial fraction of the 231 added isobutene dissolved in the liquid phase. Preferably, at 232 least about 5% of the liguid phase should be isobutene. 233 Normally the reaction is carried out at pres~ures from l00 to 235 5000 psig, with 200 to 2000 psig being preferred. The higher 236 pressures are required for high reaction temperatures, although 237 high pressures may also be used at lower reaction temperatures. 238 Preferably aqueous formaldehyde is used in the reac- 239 tion. Formaldehyde is economically available in an agueous 240 solution (formalin), typically containing 37% formaldebyde and 241 about S2-63 weight percent water. A preferred aqueous 243 formaldehyde is that disclosed in ASTM D2578-68. Other agueous 244 solutions of formaldehyde can be used with ~idely varying 245 amounts of formaldehyde and water. Preferably at least 30 246 weight percent of the formaldehyde solution is ~ater. It is 248 preferred to use agueous formaldehyde not only because it is 249 economically available, but also because water has some bene- 250 ficial effect on the reaction. Commercially available 252 formaldehyde solutions normally contain small amounts of formic 253 acid and from l to 10% methanol as a stabilizer. These small 255 amounts of methanol do not have to be removed from the formal- 256 dehyde prior to reaction. 257 In the preferred recycle embodiment of the invention, 258 illustrated in FIGS. l and 2, anhydrous formaldehyde (parafor- 259 maldehyde) is suitable, if water is initially charged to the 260 104335~
reactor and not removed from the recycle stream. Because of 262 the high costs of paraformaldehyde, however, it is preferred to 263 start with agueous formaldehyde and at least partially 264 dehydrate the recycle stream.
In addition to the small amounts of formic acid nor- 265 mally contained in commercially available formaldehyde, small 266 amounts of methanol and formic acid are formed during the reac- 267 tion by decomposition of formaldehyde, particularly when the pH 268 of the mixture is greater than 7. ~ormic acid causes formal- 270 dehyde solutions to be acidic (pH <4.0), and these acidic 271 conditions lower the yields of the diols. Thus, to minimize 273 the formation and the effect of formic acid on the reaction, it 274 has been found that the pH of the reaction mixture must be 275 maintained from about 4.0 to 7.0, as measured by standard glass 276 and calomel electrodes at ambient temperature and pressure. 278 Preferably the pH is maintained from 5.0 to 6.0 279 during the reaction. The pH of the reaction mixture is 281 maintained within the 5.0 to 6.0 level by the addition of from 282 O.Ol to 5, preferably from 0.5 to l.0, weight percent of 283 suitable buffers based on the aqueous formaldehyde solution. 285 The buffer is made up of a weak acid and the salt of a weak 287 acid. Preferably the buffers are mixtures of polybasic acids 289 and salts of polybasic acids. By weak acids, it is meant those 290 acids which have a pKa larger than 2.8. The buffers may be 292 either inorganic or organic compounds or mixtures thereof. 293 Satisfactory inorganic buffer systems include mixtures of dihy- 294 drogen sodium phosphate and disodium hydrogen phosphate, the 295 same mixture of potassium salts, etc. Some organic buffer 297 systems include monopotassium orthophthalate, monosodium 299 citrate, etc. nixtures of disodium hydrogen phosphate with 300 citric acid or diglycolic acid are the preferred buffers. 301 Small amounts of ammonia, from 0.02~ by weight of the 302 formaldehyde solution to 0.6%, are also effective in main- 303 taining the pH in the desired range. Also, acid-ammonia combi- 304 nations can be used, for example: ~aH2PO4-NH3, phthalic acid- 306 NH3.
The reaction can be carried out in the presence of 307 various solvents which can be utilized to change the critical 308 temperature of the mi~ture and increase the solutility of the 309 isobutene in the reaction mixture. Suitable solvents iDclude 311 methanol, ethanol, isopropyl alcohol, isobutanol, dioxane, 312 etc., with the lower alcohols being preferred. Isopropyl 314 alcohol is preferred, if a solvent is used. The amount of 315 vater in the reaction mixture can also be varied greatly to 316 change the critical temperature and the solubility of the 317 isobutene.
Reaction time is, of course, dependent upon reaction 318 temperatures, and is varied so as to obtain desired yields of 319 diols. Diol yields are readily determined with a liguid-gas 320 chromatograph. ~ithin the preferred temperature range of 180 321 to 250C., a reaction time from 5 to l80, preferably 30 to 90, 322 minutes is preferred. 323 The formaldehyde reacts with both isobutene and 3- 325 methyl-3-buten-l-ol, as shown in equations I and II. The mol 326 ratio of formaldehyde to 3-methyl-3-buten-l-ol charged may vary 327 widely within the scope of the invention. Usually a mol ratio 328 of formaldehyde to 3-methyl-3-buten-l-ol in the range O.l- 329 2.0:1, respectively, is satisfactory. The range 0.4-l.O:l.0 is 331 preferred.
The amount of isobutene added to the reaction mixture 332 can vary widely within the scope of the invention. Even small 334 amounts of from 5 to lO weight percent isobutene in the 335 reaction solution increases the yields of the diols. The 336 _ g _ amount of isobutene added must be at least 5 weight percent 337 based on the total charge. Preferably, however, from 20 to 40 339 weight percent is isobutene. By "weight percent isobutene" is 340 meant the weight percentage of isobutene relative to the total 341 weight of the aqueous formaldehyde, 3-methyl-3-buten-l-ol and 343 isobutene. Larger quantities of isobutene can also be used. 345 In the preferred recycle embodiment of the invention, 346 the mol ratio of formaldehyde:(isobutene ~ 3-methyl-3-buten-l- 347 ol~ will vary from 0.1-2.0:1.0, with a preferred ratio of 0.2- 348 0.8:l.
The alkenediols are separated from the reaction 349 mixture using conventional distillation techniques. In a 351 contin~ous distillation the alkenediols and high-boiling by- 352 products are taken off as bottoms, and the isobutene, water, formaldehyde and 3-methyl-3-buten-l-ol and some internediate 353 products are taken off overhead and recycled to the reactor 354 after partial dehydration. 355 The water is separated (salted out) by adding a 356 concentrated aqueous potassium carbonate solution(approximately 358 70% K2CO3~ in a weight about equal to the weight of the water 359 present in the reaction product. ~hen isopropyl alcohol is 361 used as a solvent, the 3-methyl-3-buten-l-ol and isopropyl 362 alcohol are almost insoluble at 22-26C. in a solution of egual 363 weights of X2CO3 and vater, and thus the water-K2CO3 solution 364 can be phase-separated from the alcohols. ~hen methanol is 366 used as a solvent, the methanol must be removed by distillation 367 before salting out the vater.
In the recycle embodiment of the invention, other 368 distillations and/or phase separations can be utilized to 369 reduce the guantity of water in the recycle stream or to 370 further purify the crude alkene-l,5-diol product. A bleed 372 stream can be utilized to prevent the buildup of any by- 373 products.

FIG. 1 is a schematic flow diagram of the preferred 378 recycle embodiment of the invention. In the drawing, isobutene 381 and the formalin-buffer solution are charged to reaction zone 3 382 via lines 1 and 2, respectively. The reaction product is 383 charged via line 4 to separation zone 5, wherein the desired 384 alkene-1,5-diols are separated from the reaction product and 385 removed via line 6, while the isobutene, formaldehyde and 3- 386 methyl-3-buten-1-ol are separated and recycled to the reaction 387 zone via line 7, and all or a portion of the water is separated 388 and removed via line 8.
In a preferred embodiment, a continuous longitudinal 389 or plug-flow-type reactor rather than a batch-type reactor is 390 utilized. In this preferred embodiment, the product is 392 separated into two or more portions by use of a conventional 393 distillation column. 394 FIG. 2 is a more particular schematic flow diagram of 395 the preferred recycle embodiment of the invention. In the 396 dra~ing, isobutene and the formalin-buffer solution are charged 398 to reactor 11 through lines 9 and 10, respectively. Tbe 399 reaction product is charged via line 12 to distillation column 400 13, vhere the reaction product is separated into an overhead 401 isobutene fraction, vhich is recycled via line 22, and a 402 bottoms fraction 14. Agueous K2CO3 is added via line 15 to the 403 bottoms fraction, and a phase separation occurs in settler 16. 404 A water-R2CO3-buffer phase is removed via line 17, and an 406 alcohol-water phase is fed via line 18 to second distillation 407 column 19, wherein an overhead fraction of 3-methyl-3-buten-1- 408 ol and vater is recycled via line 21 to reactor 11. The 410 ~0433S8 bottoms fraction, which contains the desired alkene-1,5-diols, is discharged via line 20. - 411 The attached figures are but schematic drawings of 412 preferred embodiments, and it is obvious that various modifi- 413 cations of the flow scheme can be made by one skilled in the 415 art.
In this single-stage, preferred embodiment, no make- 417 up 3-methyl-3-buten-l-ol is necessary, as each mol of this alcohol consumed is replaced by another mol formed from the 418 reaction of one mol of isobutene with one mol of formaldehyde. 419 By carring out the reactions in this manner, one 420 avoids the added expense of two reactors, in the first of which 422 3-methyl-3-buten-l-ol is formed according to eguation I and is 423 then separated from the reaction mixture and reacted with 424 formaldehyde in a second reactor according to equation II. 426 The following examples will serve to illustrate the 428 invention, but they are not considered to be limiting.

Example_l -- Reaction of Formaldehyde and 3-Methyl- 432 3-Buten-l-ol in the Presence of Added Isobutene 433 Example l illustrates the process of the invention in 435 which increased yields of diols result from the addition of 436 isobutene. 437 A 3.7-liter autoclave was charged with 720 g (8.36 439 mols) of 3-methyl-3-buten-l-ol, 700 g of isopropyl alcohol, 205 441 g of 36.2~ formalin, 338 g (6.04 mols) of isobutene, 3.5 g of 442 disodium hydrogen phosphate and l.3 g of diglycolic acid. The 443 formalin-buffer solution has a pH of 6.l. The autoclave was heated to 215C. and an additional 415 g of 36.2% formalin 444 solution was pumped into the autoclave over a 25-minute period 445 (total amount of formaldehyde 7.48 mols). The autoclaYe was 447 stirred and heated at 215C. for 65 minutes more. During this 448 1(143358 time, the pressure decreased from an initial value of 2100 to 449 1600 psig. The reactor was cooled and 136 g of isobutene was 450 bled off. The liquid reaction mixture vas distilled to give an 451 additional 99 g of isobutene, for a total recovery of 235 g 452 (4.215 mols) of isobutene. The remainder of the reaction 454 product contained 690 g (8.04 mols) of 3-methyl-3-buten-1-ol 455 and 259 g (2.24 mols) of alkene-1,5-diols. No formaldehyde was 457 recovered. The pH of the final reaction product was 5.4. 4S8 The following summary is based on the above data: 459 Diol Yield (~lol %) Based on:
Isobutene &
Charged Recovered Converted 3-Methyl-3- Formal-Component (Grams) (Grams) (Grams)(Mols) buten-l-ol dehyde Isobutene 338 235 103 1.84 3-l~ethyl-3-buten-l-ol 725 690 35 0.41 Formaldehyde 2240 224 7.48 Alkene-1,5-Diols 0 259 - _ 99.51 54.22 Yield = [(mols diols) . (mols isobutene converted + mols of 3-methyl-3-buten-1-ol converted)] x 100 = (2.24 . 2.25)100 =
99.5 mol ~.
2Yield = [(mols of formaldehyde converted to diol) . (mols formal-dehyde converted)] x 100 = [(2 x mols isobutene converted +
mols 3-methyl-3-buten-1-ol converted) . (mols formaldehyde converted)] x 100 = [(2 x 1.84 + 0.41) . 7.48] x 100 =
54.2 mol %.

In simultaneous reactions, as illustrated in equation 462 III and Example 1, yields based on any one of the reactants 463 isobutene, formaldehyde and 3-methyl-3-buten-1-ol can be diffi- 464 cult to determine, because the 3-methyl-3-buten-1-ol is both a 465 reactant and a product. These yields are difficult to deter- 467 mine, because one cannot tell vhether: (1) the isobutene 469 reacted vith 1 mol of formaldehyde forming 3-methyl-3-buten-1- 470 ol; (2) isobutene reacted with 2 mols of formaldehyde forming 471 the desired alkenediols; (3) the charged 3-methyl-3-buten-1-ol 472 reacted vith 1 mol of formaldehyde, forming the desired alkene- 473 ~043358 diols; or (4) the isobutene or charged 3-methyl-3-buten-l-ol 474 reacted to form some undetermined by-product. 476 However, in the above example essentially all of the 478 converted isobutene and 3-methyl-3-buten-l-ol are recovered in 479 the product diol, and thus the yield of alkene-l,5-diols based on 3-methyl-3-buten-l-ol or isobutene is essentially lO0 mol 481 percent.
~xample 2 -- Reaction of Formaldehyde and 3-Methyl- 484 3-buten-l-ol Without Added Isobutene 485 Example 2 is a comparative example illustrating the 487 reaction of equation II wherein the reaction of 3-methyl-3- 488 buten-l-ol and formaldehyde is carried out in the absence of 490 added isobutene. 491 The same reactor as Example l was charged ~ith lllO g 492 (12.9 mols) of 3-methyl-3-buten-l-ol, 230 g (8.6 mols) of 36.5~ 493 formalin, 700 g of isopropyl alcohol, 3.5 g of disodium hydro- 494 gen phosphate and l.3 g of diglycolic acid. The formalin- 496 buffer solution had a pH of 5.9. This mixture was stirred and 497 heated until a temperature of 215C. was reached. Then an 499 additional 470 g of 36.5~ formalin was pumped in for a total of 500 8.53 mols of formaldehyde. The mixture was stirred and heated 501 at 215C. for an additional 65 minutes. During this time, the 503 pressure was in the range 300-500 psig. The reactor was then 504 cooled and the contents were analyzed. The reaction product 505 contained 575 g (6.7 mols) of 3-methyl-3-buten-l-ol and 356 g 506 (3.07 mols) of alkene-1,5-diols. No formaldehyde was 507 recovered. The following summary is based on the above data: 508 Diol Yield (Mol %) Based on:
Charged Recovered Converted 3-Methyl-3- Formal-Component (Grams) (Grams) (Grams)(Mols) buten-l-ol dehyde 3-~lethyl-3-Buten-l-ollllO 575 535 6.2 - -Formaldehyde 256 0 256 8.53 ~lkene-l,5-Diols 0 356 - - 49.5 36 A comparison of the results of Examples l and 2 shows 511 that the presence of isobutene doubles the molar yield of 512 alkene-1,5-diols from 3-methyl-3-buten-l-ol. 513 ExamPl__ -- Reaction of Isobutene and Formaldehyde 516 ~ithout Added 3-Methyl-3-buten-l-ol 517 Example 3 is a comparative example illustrating the 519 reaction of formaldehyde and isobutene according to equation I. 520 The example was performed so that the yields from Examples 2 522 and 3 could be combined, illustrating the yields obtained in a 524 two-step process according to equatlons I and II, as compared 525 to the process of the invention as illustrated in equation III. 526 The same apparatus as in Example l was charged with 527 500 g of isopropyl alcohol and 789 g (14.l mols) of isobutene. 529 After a temperature of 210C. ~as reached, a solution of 3.5 g 531 of disodium hydrogen phosphate ana l.3 g of diglycolic acid in 532 620 g (7.5 mols) of 36.2% formalin ~as pumped in over a 15- 533 minute period. The formalin-buffer solution had a pH of 6.l. 534 This mixture was stirred and heated at 215C. for an additional 536 20 minutes. During this time, the pressure was maintained 538 ~ithin the range of 1600-2000 psig by the addition of 202 g of 539 isopropyl alcohol. Periodically, small samples were removed 540 and analyzed. There ~as no change in composition after 60 541 minutes. The reaction mixture was cooled and bled to give 553 542 g (9~9 mols) of isobutene. The pH of the final reaction 544 product ~as 5.25. The remainder of the product contained 316 g 545 (3.7 mols) of 3-methyl-3-buten-l-ol and 62.5 g (0.54 mols of 546 alkene-1,5-diols. ~he following summary is based on the above 548 data.
Charged Recovered Converted Yield, Mol %, Based on Component (Grams) (GramsJ (Grams)(Mols) Isobutene Formaldehyde Isobutene 789 553 236 4.2 - -Formaldehyde 224 0 224 7.5 3-Methyl-3-Buten-l-ol 0 316 - - 88 49 Alkene-l,5-Diols 0 62.6 - - 12 7 Combining Examples 2 and 3 as a two-step process for 551 the production of alkene-1,5-diols predicts the following 552 results: 553 Ultimate alkene-1,5-diol yield based on isobutene 556 converted: 557 Yield = yield of diol (Example 3) ~ tyield of 3-methyl- 558 3-buten-l-ol (Example 3) x yield of diol based 559 on 3-methyl-3-buten-l-ol (Example 2)] = 560 12 + (99 x 49.5) = 55.5% (mol) 561 Similarly, the ultimate yield of alkene-l,5-diol 564 based on formaldehyde converted: 565 7 ~ (49 x 35.8) = 24.5% (molJ 566 In a cyclic process, as shown in FIGS. l and 2, 569 wherein the reactor is continuously charged with isobutene, 570 formaldehyde and recycle 3-methyl-3-buten-l-ol, the yields of 571 alkene-l,5-diols will be as in Example l, essentially guanti- 572 tative, based on isobutene. 573 Other examples were carried out in essentially the 574 same manner as described in Example l. These examples are 576 given in Table I.

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Ex_mpl 7 -- Reaction of 3-Nethyl-3-buten-1-ol 588 with Formaldehyde in the Presence of Added Isobutene 589 A 14-ml-capacity microbomb was charged with 1.8 g 591 (0.02 mol) of 3-methyl-3-buten-1-ol and 1.61 g (0.02 mol) of 592 37.8% aqueous formaldehyde containing 0.005 g each of disodium 595 hydrogen phosphate and monosodium dihydrogen phosphate. The pH 596 of this solution was 6.9. Then 1.09 g (0.02 mol) of isobutene 597 was charged. The bomb was sealed and heated for 2 hours at 598 200C. After cooling, the bomb was opened, the unreacted iso- 599 butene was removed and measured, and the liquid reaction 601 mixture ~as analyzed by vapor-phase chromatography, using n- 602 octanol as an internal standard. The vapor-phase chromatograph 604 indicated the reaction mixture contained, by weight percent: 605 36% 3-methyl-3-buten-1-ol and 20% alkene-1,5-diols. 606 - lô -

Claims (11)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a process for the production of alkene-1,5-diols comprising:
(1) contacting in a reaction zone a reaction mixture comprising 3-methyl-3-buten-1-ol and aqueous formaldehyde, (2) reacting said mixture at an elevated temperature and pressure, said temperature being below the critical temperature of said reaction mixture;
the improvement comprising effecting said reaction in the presence of at least 5 wt. %, based on the total charge of added isobutene.

2. A process in accordance with Claim 1 wherein from 5 to 40% by weight of said mixture is added isobutene.

3. A process in accordance with Claim 2 wherein the pH of said reaction mixture is maintained from 4.0 to 7Ø

4. A process in accordance with Claim 3 wherein the pH of said reaction mixture is maintained from 4.0 to 7.0 by the addition of a buffer comprising a weak polybasic acid and the salt of a weak polybasic acid.

5. A process in accordance with Claim 1 wherein said reaction is carried out at a temperature from 180° to 250°C. and at a pressure from 200 to 2000 psig, and wherein from 20 to 40 weight percent of said mixture is added isobutene, and the pH of said reaction mixture is main-tained from 5.0 to 6Ø

6. A process for the production of alkene-1,5-diols comprising:
(1) contacting in a reaction zone a mixture comprising:

(a) 3-methyl-3-buten-1-ol, (b) aqueous formaldehyde, and (c) isobutene, said isobutene comprising from 5 to 40 weight percent of said mixture;
(2) reacting said mixture at a temperature from 150° to 300°C. and at a pressure from 100 to 5000 psig for a period of time sufficient to form a reaction product containing said alkene-1,5-diols, said temperature being below the critical temperature of said mixture;
(3) separating from said reaction product a first portion comprising said alkene-1,5-diols and a second portion com-prising formaldehyde, water, isobutene and 3-methyl-3-buten-1-ol; and (4) recycling said second portion to said reaction zone.

7. A process in accordance with Claim 6 wherein the pH
of said reaction mixture is maintained from 4.0 to 7Ø

8. A process in accordance with Claim 6 wherein the pH
of said reaction mixture is maintained from 5.0 to 6.0 by the addition of a buffer comprising a weak polybasic acid and salt of a weak polybasic acid.

9. A process in accordance with Claim 6 wherein aqueous formaldehyde is fed to said reaction zone and said second por-tion is partially dehydrated prior to said recycling.

10. A process in accordance with Claim 6 wherein said reaction is carried out at a temperature from 180° to 250°C.
and at a pressure from 200 to 2000 psig, and wherein the pH of said reaction mixture is maintained from 5.0 to 6.0, and from 20 to 40 weight percent of said mixture is isobutene.

11. A process for the production of alkene-1,5-diols comprising:
(1) contacting in a reaction zone a mixture comprising:
(a) 3-methyl-3-buten-1-ol, (b) aqueous formaldehyde, and (c) isobutene, said isobutene comprising from 20 to 40 weight percent of said mixture;
(2) reacting said mixture at a temperature from 180° to 250°C. and at a pressure from 200 to 2000 psig for a period of time sufficient to form a reaction product containing said alkene-1,5-diols, said temperature being below the critical temperature of said mixture, and wherein the pH of said reaction mixture is maintained from 5.0 to 6.0 by the addition of a buffer comprising a weak polybasic acid and the salt of a weak polybasic acid;
(3) separating from said reaction product a first portion comprising isobutene and recycling said first portion to said reaction zone;
(4) separating from said reaction product a second portion comprising water;
(5) separating from said reaction product a third portion comprising 3-methyl-3-buten-1-ol and recycling said third portion to said reaction zone; and (6) separating from said reaction product a fourth portion comprising said alkene-1,5-diols.