This application is a 371 of PCT/JP00/03130, filed May 16, 2000, now WO00/69799, published Nov. 23, 2000. 
The present invention relates to a method for producing 3-alkoxyalkanol precursors, and to a method for producing 3-alkoxyalkanols.  More precisely, the invention relates to a method for producing a 3-alkoxyalkanol precursor mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal; to a method for producing a 3-alkoxyalkanal precursor, 1,1,3-trialkoxyalkane; to a method for producing a 3-alkoxyalkanol precursor, 3-alkoxyalkanal; and to a method for producing a 3-alkoxyalkanol. 
For producing 3-alkoxyalkanols such as 3-methoxypropanol, which are useful for solvents for paints and photoresists and for materials for chemical products, heretofore known are  less than 1 greater than  a method of reacting trimethylene glycol with a metal followed by reacting the resulting sodium alkoxide with an alkyl halide (J. Am.  Chem.  Soc.,  65, 1276, 1943);  less than 2 greater than  a method of reacting 3-chloro-1-propyl alcohol with a metal alkoxide (Japanese Patent Laid-Open No.  113546/1996); and  less than 3 greater than  a method of decomposing a diazonium salt obtained from an aminoether (Japanese Patent Laid-Open No.  316605/1998).  However, the starting materials for these methods are difficult to obtain, and the practicability of the methods is therefore low. 
Another method  less than 4 greater than  for which the starting materials are easy to obtain is known.  The method comprises hydrogenating a reaction product, which is obtained through reaction of acrolein and methanol in the presence of a basic catalyst, followed by reacting the resulting hydrogenate with acetic acid in the presence of an acid catalyst to give 3-methoxy-1-acetoxypropane (Japanese Patent Laid-Open No.  25821/1995).  The patent publication says that the reaction of acrolein with methanol in the presence of a basic catalyst gives a reaction product containing 3-methoxypropylaldehyde, and that the hydrogenation of the reaction product gives a liquid reaction product containing 3-methoxypropanol.  However, the method  less than 4 greater than  requires a basic catalyst and therefore requires accurate and delicate reaction control.  Another drawback of the method is that the yield of 3-alkoxyalkanol therein is low. 
The present invention is to solve the drawbacks of the prior-art methods as above, and to provide an efficient and high-yield method for producing 3-alkoxyalkanols and their precursors. 
The invention includes four aspects, first to fourth aspects. 
The first aspect of the invention is to provide an efficient and high-yield method for producing a 3-alkoxyalkanol precursor mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal.  Another object of the first aspect is to provide an efficient and high-yield method for producing a 3-alkoxyalkanol precursor, 3-alkoxyalkanal, from the mixture.  Still another object is to provide an efficient and high-yield method for producing the 3-alkoxyalkanol, a final product, from an xcex1,xcex2-unsaturated aldehyde and an alcohol. 
The second aspect of the invention is to provide an industrial method for producing a 3-alkoxyalkanal.  Another object of the second aspect is to provide a method for producing a 3-alkoxyalkanol of high purity. 
The third aspect of the invention is to provide an industrial method for producing a 3-alkoxyalkanol. 
The forth aspect of the invention is to provide an industrial method for producing a 3-alkoxyalkanol of high purity.  Another object of the fourth aspect is to provide a method for producing a 1,1,3-trialkoxyalkane and a 3-alkoxyalkanal that give such a 3-alkoxyalkanol. 
We, the present inventors have assiduously studied so as to attain the objects of the first aspect of the invention, and, as a result, have found that the objects can be attained by reacting an xcex1,xcex2-unsaturated aldehyde with an alcohol in the presence of an acid catalyst followed by hydrolyzing the resulting reaction product and then hydrogenating it.  On the basis of this finding, we have completed the first aspect of the invention. 
To attain the objects of the second aspect of the invention, we, the inventors have assiduously studied on the premise of direct use of oxidized products of propylene or isobutylene, and, as a result, have found that the objects can be attained by distilling a liquid reaction product of acrolein or methacrolein with an alcohol to collect an azeotropic mixture of 3-alkoxyalkanal with water from it, followed by hydrogenating the thus-obtained 3-alkoxyalkanal.  On the basis of this finding, we have completed the second aspect of the invention. 
To attain the objects of the third aspect of the invention, we, the inventors have specifically noted a step of hydrolysis and a step of hydrogenation of a mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal, and have assiduously studied them.  As a result, we have found that the objects can be attained by simultaneously hydrolyzing and hydrogenating the mixture, and, on the basis of this finding, we have completed the third aspect of the invention. 
To attain the objects of the fourth aspect of the invention, we, the inventors have specifically noted the treatment of the oxidation product gas of propylene or isobutylene, and have assiduously studied it.  As a result, we have found that the objects can be attained by contacting the oxidation product gas of propylene or isobutylene with an alcohol in a specific condition, and, on the basis of this finding, we have completed the fourth aspect of the invention. 
Specifically, the present invention provides the following:
(1) A method for producing a mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal, which comprises reacting an xcex1,xcex2-unsaturated aldehyde with an alcohol in the presence of an acid catalyst;
(2) A method for producing a 3-alkoxyalkanal, which comprises hydrolyzing the mixture produced in the method of above (1);
(3) A method for producing a 3-alkoxyalkanol, which comprises hydrogenating the 3-alkoxyalkanal produced in the method of above (2);
(4) A method for producing a 3-alkoxyalkanal, which comprises distilling a liquid reaction product of acrolein or methacrolein obtained through oxidation of propylene or isobutylene and containing acids, with an alcohol, to thereby collect an azeotropic mixture of a 3-alkoxyalkanal with water;
(5) A method for producing a 3-alkoxyalkanol, which comprises hydrogenating the 3-alkoxyalkanal produced in the method of above (4);
(6) A method for producing a 3-alkoxyalkanol, which comprises simultaneously hydrolyzing and hydrogenating a reaction mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal obtained through reaction of an xcex1,xcex2-unsaturated aldehyde with an alcohol;
(7) A method for producing a 1,1,3-trialkoxyalkane, which comprises reacting acrolein gas or methacrolein gas obtained through contact of an oxidation product gas of propylene or isobutylene with an alcohol capable of almost completely vaporizing in the system, with an alcohol;
(8) A method for producing a 3-alkoxyalkanal, which comprises hydrolyzing the 1,1,3-trialkoxyalkane produced in the method of above (7);
(9) A method for producing a 3-alkoxyalkanol, which comprises hydrogenating the 3-alkoxyalkanal produced in the method of above (8); and
(10) A method for producing a 3-alkoxyalkanol, which comprises simultaneously hydrolyzing and hydrogenating the 1,1,3-trialkoxyalkane produced in the method of above (7). 
Embodiments of the invention are described below. 
First described is the first aspect of the invention.  It includes three embodiments.  The first embodiment is a method for producing a mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal, and it comprises reacting an xcex1,xcex2-unsaturated aldehyde with an alcohol in the presence of an acid catalyst. 
The acid catalyst to be used in this first aspect is not specifically defined.  For this, however, preferred are mineral acids such as sulfuric acid and hydrochloric acid; and solid catalysts such as strong-acidic ion-exchange resins.  Of those, especially preferred is a catalyst of strong-acidic ion-exchange resins as the catalyst separation from reaction mixtures is easy. 
The amount of the catalyst to be used is not also specifically defined.  In general, it falls between 0.0001 and 10 equivalents in terms of acid, but preferably between 0.001 and 1 equivalent, relative to the xcex1,xcex2-unsaturated aldehyde.  If the amount is smaller than 0.0001 equivalents, the reaction speed will be low; but if larger than 10 equivalents, it is unfavorable, since such a large amount of the catalyst used could no more augment the intended effect and the catalyst loss increases. 
The reaction of the first embodiment may be effected in any mode of flow systems, batch systems or semi-batch systems.  The amount of the catalyst to be used in flow-system reaction may be such that the reactants, xcex1,xcex2-unsaturated aldehyde and alcohol are well contacted with the catalyst.  Satisfying this condition, the amount of the catalyst for it may be suitably selected from the ordinary range of catalyst amount as above. 
The xcex1,xcex2-unsaturated aldehyde to be used in the first aspect of the invention is an aldehyde represented by the following general formula (1):
R1xe2x80x94CHxe2x95x90CR2xe2x80x94CHOxe2x80x83xe2x80x83(1)
wherein R1 and R2 each independently indicate a hydrogen atom or an alkyl group.  Concretely, preferred examples of the aldehyde are acrolein, methacrolein and crotonaldehyde.  The xcex1,xcex2-unsaturated aldehyde may contain water not interfering with its reaction with an alcohol. 
The alcohol is not specifically defined, represented by the following general formula (2):
R3xe2x80x94OHxe2x80x83xe2x80x83(2)
wherein R3indicates an alkyl group.  Concretely, for example, it includes methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, and t-butanol. 
In the first embodiment of the first aspect of the invention, the xcex1,xcex2-unsaturated aldehyde and alcohol both mentioned above are reacted in the presence of the acid catalyst also mentioned above to produce a 3-alkoxyalkanol precursor mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal. 
Concretely, for example, produced are a mixture of 1,1,3-trimethoxypropane and 3-methoxypropanal; a mixture of 1,1,3-triethoxypropane and 3-ethoxypropanal; a mixture of 1,1,3-tripropoxypropane and 3-propoxypropanal; a mixture of 1,1,3-triisopropoxypropane and 3-isopropoxypropanal; and a mixture of 1,1,3-trimethoxy-2-methylpropane and 3-methoxy2-methylpropanal. 
The condition for the reaction of such an xcex1,xcex2-unsaturated aldehyde and an alcohol is not specifically defined.  Regarding the amount of the two to be reacted, the molar ratio of alcohol/xcex1,xcex2-unsaturated aldehyde may fall generally between 1 and 15, but preferably between 3 and 10.  If the molar ratio is smaller than 1, heavy matters will be formed and the selectivity of the intended products in this embodiment, 1,1,3-trialkoxyalkane and 3-alkoxyalkanal will decrease.  On the other hand, if it is larger than 15, too much alcohol used could no more augment the intended effect, and its loss increases meaninglessly.  Using too much alcohol is unfavorable from the economical aspect. 
The reaction temperature may fall generally between 0 and 120xc2x0 C., but preferably between 10 and 100xc2x0 C. If the reaction temperature is lower than 0xc2x0 C., the reaction speed will be low; but if higher than 120xc2x0 C., it is unfavorable, since heavy matters will increase and the selectivity of the intended products will lower. 
The reaction finishes within 24 hours, but the time for the reaction preferably falls between 0.1 and 10 hours.  If the reaction time is too short, the conversion of the xcex1,xcex2-unsaturated aldehyde will lower; but if too long, it is unfavorable, since side products will increase and the selectivity of the intended 1,1,3-trialkoxyalkane and 3-alkoxyalkanal will lower. 
The reaction may be effected under atmospheric pressure or under increased pressure. 
The second embodiment of the first aspect of the invention is for producing a 3-alkoxyalkanal by hydrolyzing the reaction mixture produced in the first embodiment thereof. 
Precisely, this is a method for converting the 1,1,3-trialkoxyalkane into a 3-alkoxyalkanol precursor, 3-alkoxyalkanal, by hydrolyzing the 3-alkoxyalkanol precursor mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal. 
Concretely, 3-methoxypropanal, 3-ethoxypropanal, 3-propoxypropanal, 3-isopropoxypropanal, 3-methoxy-2-methylpropanal and the like are produced in the method. 
In this embodiment, the alkoxyalkanol precursor mixture is hydrolyzed while removing alcohol through distillation, whereby almost all the precursor mixture is converted into a 3-alkoxyalkanal.  In the step of hydrolysis, it is undesirable to decompose the 3-alkoxyalkanal into the stage of xcex1,xcex2-unsaturated aldehyde.  This embodiment is characterized in that the amount of the 3-alkoxyalkanal decomposed into the stage of xcex1,xcex2-aldehyde is reduced. 
In the step of hydrolysis, using a catalyst is preferred.  The catalyst may be any ordinary acid catalyst for hydrolysis, including, for example, mineral acids such as sulfuric acid and hydrochloric acid, organic acids such as acetic acid, and solid acids such as acidic ion-exchange resins. 
The amount of the catalyst to be used is not specifically defined, generally falling between 0.0001 and 10 equivalents interms of acid, but preferably between 0.001 and 1 equivalent, relative to the 1,1,3-trialkoxyalkane.  If the amount is smaller than 0.0001 equivalents the hydrolysis speed will be low; but even if larger than 10 equivalents, such a large amount of the catalyst used could no more augment the intended effect of hydrolysis. 
The condition for hydrolysis is not also specifically defined.  The temperature, the pressure and the time for it may be any ordinary ones. 
The temperature may fall generally between 0 and 200xc2x0 C., but preferably between 10 and 150xc2x0 C. If it is lower than 0xc2x0C., the hydrolysis speed will be low; but if higher than 200xc2x0 C., it is unfavorable, since the precursor mixture will be decomposed to the stage of xcex1,xcex2-unsaturated aldehyde and the selectivity of the intended 3-alkoxyalkanal will lower. 
The hydrolysis finishes within 10 hours, but the time for it is preferably not longer than 5 hours.  Too long reaction time for it is unfavorable, since side products will increase and the selectivity of the intended 3-alkoxyalkanal will lower.  The amount of water to be present in the reaction zone may well be equivalent or more relative to the 1,1,3-trialkoxyalkane, but is generally up to 20 equivalents.  If the amount of water is smaller than the equivalent thereto, the 1,1,3-trialkoxyalkane could not be hydrolyzed sufficiently; but if larger than 20 equivalents, it is unfavorable, since an additional step of post-treating the product for separating water from it will be needed and the step increases the energy costs for the method. 
The third embodiment of the first aspect of the invention is for producing a 3-alkoxyalkanol, and it comprises hydrogenating the 3-alkoxyalkanol precursor, 3-alkoxyalkanal produced in the second embodiment mentioned above. 
Concretely, this is for producing 3-methoxypropanol, 3-ethoxypropanol, 3-propoxypropanol, 3-isopropoxypropanol, 3-methoxy-2-methylpropanol, etc. 
In this step, the 3-alkoxyalkanol precursor is hydrolyzed in the presence of an ordinary hydrogenation catalyst such as Raney nickel, nickel/diatomaceous earth or rhodium/carbon. 
The amount of the catalyst to be used is not specifically defined, generally falling between 0.01 and 50% by weight, but preferably between 0.1 and 20% by weight of the 3-alkoxyalkanal.  If it is smaller than 0.01% by weight, the hydrogenation speed will be low; but if larger than 50% by weight, it is unfavorable, since such a large amount of the catalyst used could no more augment the intended effect and the catalyst loss increases. 
The hydrogenation temperature may fall generally between 20 and 250xc2x0 C., but preferably between 50 and 180xc2x0 C. If it is lower than 20xc2x0 C., the hydrogenation speed will be low; but if higher than 250xc2x0 C., it is unfavorable, since the precursor will be decomposed and the selectivity of the intended product, 3-alkoxyalkanol will lower. 
The pressure may fall generally between 1 and 20 MPa, but preferably between 3 and 15 MPa.  If it is lower than 1 MPa, the hydrogenation speed will be low; gut even if higher than 20 MPa, such a high pressure could no more augment the intended effect. 
The hydrogenation may be effected in any mode of flow systems, batch systems or semi-batch systems. 
Next described is the second aspect of the invention.  It includes two embodiments. 
The first embodiment of the second aspect of the invention is for producing a 3-alkoxyalkanal, and it comprises distilling a liquid reaction product of acrolein or methacrolein obtained through oxidation of propylene or isobutylene and containing acids, with an alcohol, to thereby collect an azeotropic mixture of a 3-alkoxyalkanal with water. 
The propylene or isobutylene oxidation may be effected generally in the presence of a molybdenum-bismuth composite oxide catalyst, at a temperature falling between 280 and 350xc2x0 C., for a contact time falling between 1.5 and 5.0 seconds, and its reactivity to give acrolein or methacrolein falls between 90 and 97%. 
The unit flow yield of acrolein or methacrolein, or that is, the yield thereof in one pass of propylene or isobutylene into the reactor filled with the catalyst falls between 70 and 80%.  In general, from 5 to 10% of acids such as acetic acid and acrylic acid are formed as side products in the process of oxidation.  Accordingly, the oxidation product contains the acids. 
One characteristic feature of this embodiment is that the acrolein or methacrolein produced through the step of oxidation and therefore containing the acids formed as side products in the step is directly reacted with an alcohol in the next step. 
The alcohol to be used for the reaction is not specifically defined, including, for example, methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol and t-butanol. 
In the reaction of acrolein or methacrolein with such an alcohol in this embodiment, generally used is a catalyst. 
The catalyst to be used is not specifically defined, including, for example, mineral acids such as sulfuric acid and hydrochloric acid, solid catalysts such as acidic ion exchange resins, as well as basic catalysts such as alkali metals, alkaline earth metals and their hydroxides.  Of those, preferred are acidic solid catalysts such as strong-acidic ion-exchange resins, as they are easy to separate and they are stable. 
The amount of the catalyst to be used is not also specifically defined, generally falling between 0.0001 and 10 equivalents, but preferably between 0.001 and 1 equivalent relative to acrolein or methacrolein.  If it is smaller than 0.0001 equivalents, the reaction speed will be low; but if larger than 10 equivalents, it is unfavorable, since such a large amount of the catalyst used could no more augment the intended effect and the catalyst loss increases. 
The reaction of this embodiment may be effected in any mode of flow systems, batch systems or semi-batch systems.  The amount of the catalyst to be used in flow-system reaction may be such that the reactants, acrolein or methacrolein and alcohol are well contacted with the catalyst.  Satisfying this condition, the amount of the catalyst for it may be suitably selected from the ordinary range of catalyst amount as above. 
To the ratio of the two, acrolein or methacrolein and alcohol to be reacted in this embodiment, the same as that for the molar ratio of alcohol/xcex1,xcex2-unsaturated aldehyde in the first embodiment in the first aspect mentioned above may apply for the same reason also mentioned above.  To the reaction condition including the reaction temperature, the reaction time and the reaction pressure for this embodiment, the same as those mentioned herein above for the reaction condition for alcohol and xcex1,xcex2-unsaturated aldehyde in the first embodiment of the first aspect mentioned may also apply. 
The 3-alkoxyalkanal thus produced in this embodiment includes, for example, 3-methoxypropanal, 3-ethoxypropanal, 3-propoxypropanal, 3-isopropoxypropanal, and 3-methoxy-2-methylpropanal. 
As so mentioned hereinabove, the first embodiment of the second aspect of the invention is for distilling the liquid reaction product obtained through reaction of acrolein or methacrolein, which is prepared by oxidizing propylene or isobutylene and therefore contains acids, with an alcohol, to thereby collect an azeotropic mixture of a 3-alkoxyalkanal with water. 
Specifically, this is for producing a 3-alkoxyalkanal by distilling the liquid reaction product of such an acid-containing acrolein or methacrolein and an alcohol, in the presence of water to thereby take out an azeotropic mixture of the intended 3-alkoxyalkanal with water through the top of the distillation column. 
For this, water may be added to the liquid reaction product obtained through reaction of acrolein or methacrolein with an alcohol, to thereby distill it.  For example, in case where propylene is oxidized to give acrolein, the liquid reaction product contains water.  In this case, therefore, adding water to the reaction product is unnecessary, and the reaction product may be directly distilled. 
The amount of water necessary for the distillation may well be to form the intended azeotropic mixture of a 3-alkoxyalkanal with it.  In general, it falls between 2 and 20 equivalents relative to the 3-alkoxyalkanal.  If the amount of water is smaller than 2 equivalents, the amount of the 3-alkoxyalkanal to form the azeotropic mixture to be recovered will lower; but if larger than 20 equivalents, it is uneconomical since the distillation column requires an increased number of distillation stages. 
The distillation may be effected either under atmospheric pressure or reduced pressure, but is preferably effected under reduced pressure. 
The distillation may be effected generally at a temperature not higher than 200xc2x0 C., but preferably not higher than 150xc2x0 C. If its temperature is higher than 200xc2x0 C., it is unfavorable since the 3-alkoxyalkanal will be greatly decomposed into acrolein or methacrolein owing to the influence thereon of the acids existing in the distillation system. 
The aqueous azeotropic mixture of 3-alkoxyalkanal collected in the present embodiment does not substantially contain acids.  Accordingly, when hydrogenated, it gives high-purity 3-alkoxyalkanol corresponding to it. 
The second embodiment of the second aspect of the invention is for producing a 3-alkoxyalkanol by hydrogenating the 3-alkoxyalkanal produced in the first embodiment mentioned above. 
For hydrogenating it, the aqueous azeotropic mixture does not require removal of water from it, and it may be directly processed for hydrogenation.  In this point, the industrial advantage of the method of this embodiment is obvious. 
For the catalyst and its amount to be sued, and also the reaction condition for the hydrogenation in this embodiment, referred to are the same as those mentioned hereinabove for the third embodiment of the first aspect of the invention. 
The 3-alkoxyalkanol thus obtained in this embodiment includes, for example, 3-methoxypropanol, 3-ethoxypropanol, 3-propoxypropanol, 3-isopropoxypropanol, and 3-methoxy-2-methylpropanol. 
Next described is the third aspect of the invention. 
In the third aspect, an xcex1,xcex2-unsaturated aldehyde is first reacted with an alcohol to prepare a mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal. 
The xcex1,xcex2-unsaturated aldehyde to be used in the third aspect includes, for example, acrolein, methacrolein, and crotonaldehyde.  Of those, preferred is acrolein. 
The xcex1,xcex2-unsaturated aldehyde does not require purifying.  For it, for example, oxidized gas of propylene may be directly used. 
The alcohol for use herein includes, for example, methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, and t-butanol. 
In the reaction of such an xcex1,xcex2-unsaturated aldehyde and an alcohol, generally used is a catalyst. 
The catalyst to be used is not specifically defined, and any one mentioned for the first embodiment of the first aspect of the invention is also usable herein.  For the amount of the catalyst to be used and the reaction condition for this aspect, referred to are the same as those mentioned hereinabove for the first embodiment of the first aspect of the invention. 
In the third aspect of the invention, an xcex1,xcex2-unsaturated aldehyde such as that mentioned above is reacted with an alcohol mentioned above under the condition also mentioned above to prepare a 3-alkoxyalkanol precursor mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal.  Concretely, for the mixture to be prepared herein, referred to are the same as those mentioned hereinabove for the mixture produced in the first embodiment of the first aspect of the invention. 
In the third aspect of the invention, the mixture prepared in the manner as above is then hydrolyzed while simultaneously hydrogenated.  In other words, the mixture is subjected to simultaneous hydrolysis and hydrogenation in one and the same reaction zone. 
For simultaneously hydrolyzing and hydrogenating the mixture, both a catalyst for hydrolysis and a catalyst for hydrogenation are made to exist in the reaction mixture of 1,1,3-trialkoxyalkane and 3-alkoxyalkanal obtained through reaction of the xcex1,xcex2-unsaturated aldehyde and the alcohol, and the reaction mixture is pressurized with hydrogen in that condition. 
For it, a binary catalyst having both the ability of hydrolysis and the ability of hydrogenation may be used. 
Through simultaneous hydrolysis and hydrogenation thereof, the 1,1,3-trialkoxyalkane in the mixture is converted into a 3-alkoxyalkanal, and the 3-alkoxyalkanal is immediately converted into a 3-alkoxyalkanol. 
For the 3-alkoxyalkanol to be produced in the third aspect of the invention, referred to are the same as those mentioned hereinabove for that to be produced in the third embodiment of the first aspect of the invention. 
The catalyst for hydrolysis to be used herein may be the same as that used in the second embodiment of the first aspect mentioned hereinabove.  For this, preferred are acidic solid catalysts such as ion-exchange resins as they do not cause plant corrosion. 
The catalyst for hydrolysis may be the same as that used in the step of reacting the starting xcex1,xcex2-unsaturated aldehyde and alcohol, and the catalyst still remaining in the reaction mixture of the xcex1,xcex2-unsaturated aldehyde and the alcohol may be directly used for it.  In this point, the industrial advantage of the method of the invention is remarkable. 
The amount of the catalyst to remain in the reaction system is not specifically defined, generally falling between 0.0001 and 10 equivalents, but preferably between 0.001 and 1 equivalent in terms of acid, relative to the 1,1,3-trialkoxyalkane.  If it is smaller than 0.0001 equivalents, the reaction speed will be low; but even if larger than 10 equivalents, it will no more augment the intended effect. 
The catalyst for hydrogenation may be any ordinary one, including, for example, Raney nickel, nickel/diatomaceous earth, and ruthenium/carbon.  For the amount of the catalyst to be used herein, referred to is the same as that mentioned hereinabove for the third embodiment of the first aspect of the invention. 
The amount of water to be present in the reaction zone may well be equivalent or more relative to the 1,1,3-trialkoxyalkane, but is generally up to 20 equivalents.  If the amount of water is smaller than the equivalent thereto, the 1,1,3-trialkoxyalkane could not be hydrolyzed sufficiently; but if larger than 20 equivalents, it is unfavorable, since an additional step of post-treating the product for separating water from it will be needed and the step increases the energy costs for the method. 
The condition for simultaneous hydrolysis and hydrogenation is not specifically defined, but the temperature for it generally falls between 20 and 250xc2x0 C., preferably between 50 and 180xc2x0 C. If it is lower than 20xc2x0 C., the reaction speed will be low; but if higher than 250xc2x0 C., it is unfavorable, since the selectivity of the intended product, 3-alkoxyalkanol will lower. 
For the hydrogen pressure for the reaction, referred to is the same as that mentioned hereinabove for the third embodiment of the first aspect of the invention. 
The reaction of hydrolysis and hydrogenation may be effected in any mode of flow systems, batch systems or semi-batch systems. 
Next described is the fourth aspect of the invention.  It includes four embodiments. 
The first embodiment of the fourth aspect of the invention is for producing a 1,1,3-trialkoxyalkane, and it comprises reacting acrolein gas or methacrolein gas obtained through contact of an oxidation product gas of propylene or isobutylene with an alcohol capable of almost completely vaporizing in the system, with an alcohol. 
In this, the oxidation of propylene or isobutylene gas is effected generally in the presence of a molybdenum-bismuth composite oxide catalyst, at a temperature falling between 280 and 350xc2x0 C. for a contact time falling between 1.5 and 5.0 seconds, through which the reaction yield of the product, acrolein or methacrolein falls between 90 and 97%. 
The unit flow yield of acrolein or methacrolein falls between 70 and 80%.  In general, from 5 to 10% of acids such as acetic acid, acrylic acid and methacrylic acid are formed as side products in the process of oxidation.  Accordingly, the oxidation product contains the acids, and may contain any others such as water, nitrogen, oxygen, carbon dioxide and carbon monoxide. 
This embodiment is characterized in that the oxidation product gas of propylene or isobutylene is contacted with an alcohol capable of almost completely vaporizing in the system. 
The mode of contacting the oxidation product gas with such an alcohol is not specifically defined.  Preferably used for it is a column reactor.  For example, the oxidation product gas is introduced into it through its bottom, while an alcohol is thereinto through its top, and the two are contacted with each other in a mode of countercurrent flow in the column reactor. 
While contacted with an alcohol in such a mode of countercurrent flow, a part or almost all of water in the oxidation product gas and almost all the acids therein are condensed owing to the heat of vaporization of the alcohol, and are then separated from the system. 
The alcohol to be fed into the column reactor through its top is not specifically defined.  As will be mentioned hereinunder, it is desirable that the alcohol is the same as that to be used in producing the product, 1,1,3-trialkoxyalkane through reaction of acrolein or methacrolein with it. 
The alcohol includes, for example, methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, and t-butanol.  These alcohols may be used either singly or as combined into their mixture. 
The amount of the alcohol to be fed into the column reactor through its top must be such that almost all of it can vaporize when contacted with the oxidation product gas in the reactor.  More precisely, the amount of the alcohol must be such that almost all of it can vaporize in the system and that it is enough to condense a part or all of the water existing in the oxidation product gas and almost all the acids existing therein owing to the heat of vaporization of the alcohol. 
The amount of the alcohol to be fed into the column reactor through its top is not constant but varies, depending on the water content of the oxidation product gas and also on the amount of the gas.  In general, it may fall between 50 g and 5 kg, but preferably between 200 g and 1 kg, relative to 1 m3 of the oxidation product gas. 
If the amount of the alcohol fed into the reactor is too small, the acids could not be completely removed from the oxidation product gas; but if too large, it is unfavorable, since the excess alcohol will remain in the bottom of the reactor and the loss alcohol must be recovered. 
The alcohol to be fed into the column reactor through its top is preferably pure alcohol, but it may contain minor water not interfering with the process operation.  If desired, any other component may be added to the alcohol for any specific object. 
For example, for preventing polymerization of acrolein or methacrolein, it is desirable to add a polymerization inhibitor such as hydroquinone to the alcohol. 
In that manner, the oxidation product gas of propylene or isobutylene is contacted with such an alcohol capable of almost completely vaporizing in the system, whereby an alcohol-containing acrolein or methacrolein gas is taken out through the top of the reactor and water that contains acids is through the bottom thereof. 
In this embodiment, the alcohol-containing acrolein or methacrolein gas is the starting material and this is reacted with an alcohol to produce a 1,1,3-trialkoxyalkane. 
The alcohol to be reacted with the acrolein or methacrolein may be, as so mentioned hereinabove, of the same type as that of the alcohol contacted with the oxidation product gas.  It includes, for example, methanol, ethanol, 1-propanol, isopropanol, 1-butanol, 2-butanol, isobutanol, and t-butanol. 
As in the above, the acrolein or methacrolein gas collected through the top of the column reactor contains the alcohol used for preparing it, and its advantage is that it may be directly processed, as it is, in the next step of reacting it with an alcohol. 
In the step of reacting the acrolein or methacrolein with an alcohol, generally used is a catalyst. 
The catalyst is not specifically defined, including, for example, mineral acids such as sulfuric acid and hydrochloric acid, solid catalysts such as acidic ion-exchange resins, and basic catalysts such as alkali metals, alkaline earth metals and their hydroxides.  For the catalyst, preferred are acidic solid catalysts such as strong-acidic ion-exchange resins, as they are easy to separate and they are stable. 
The amount of the catalyst to be used in the step is not also specifically defined, for which, for example, generally referred to are the same as those mentioned hereinabove for the first embodiment of the first aspect of the invention. 
For reaction mode and the reaction condition for the step, also referred to are the same as those mentioned hereinabove for the first embodiment of the first aspect of the invention. 
The 1,1,3-trialkoxyalkane obtained in the process includes, for example, 1,1,3-trimethoxypropane, 1,1,3-triethoxypropane, 1,1,3-tripropoxypropane, 1,1,3-triisopropoxypropane, and 1,1,3-trimethoxy-2-methylpropane. 
The second embodiment of the fourth aspect of the invention is for producing a 3-alkoxyalkanal, and it comprises hydrolyzing the 1,1,3-trialkoxyalkane produced in the above-mentioned first embodiment. 
To hydrolyze it, using a catalyst is preferred.  For this, referred to are the same as those mentioned hereinabove for the second embodiment of the first aspect of the invention. 
For the amount of the catalyst to be used and for the condition for the hydrolysis, also referred to are the same as those mentioned hereinabove for the second embodiment of the first aspect of the invention. 
The 3-alkoxyalkanal obtained in the process includes, for example, 3-methoxypropanal, 3-ethoxypropanal, 3-propoxypropanal, 3-isopropoxypropanal, and 3-methoxy-2-methylpropanal. 
The third embodiment of the fourth aspect of the invention is for producing a 3-alkoxyalkanol, and it comprises hydrogenating the 3-alkoxyalkanal produced in the above-mentioned second embodiment. 
The hydrogenation is effected in the presence of an ordinary hydrogenation catalyst such as Raney nickel, nickel/diatomaceous earth or ruthenium/carbon. 
For the amount of the catalyst to be used and for the condition for the hydrogenation, referred to are the same as those mentioned hereinabove for the third embodiment of the first aspect of the invention. 
The 3-alkoxyalkanol obtained in the process includes, for example, 3-methoxypropanol, 3-ethoxypropanol, 3-propoxypropanol, 3-isopropoxypropanol, and 3-methoxy-2-methylpropanol. 
The fourth embodiment of the fourth aspect of the invention is for producing a 3-alkoxyalkanol, and it comprises simultaneously hydrolyzing and hydrogenating the 1,1,3-trialkoxyalkane produced in the above-mentioned first embodiment. 
For simultaneously hydrolyzing and hydrogenating it, the 1,1,3-trialkoxyalkane produced in the first embodiment is processed with water and hydrogen in one and the same reaction zone that contains both a hydrolysis catalyst and a hydrogenation catalyst or contains a binary catalyst having both the ability of hydrolysis and the ability of hydrogenation. 
Simultaneously hydrolyzed and hydrogenated in that manner, the 1,1,3-trialkoxyalkane is converted into a 3-alkoxyalkanal corresponding to it, and the resulting 3-alkoxyalkanal is then immediately converted into a 3-alkoxyalkanol corresponding to it. 
For the hydrolysis catalyst, herein usable are acid catalysts such as those used in the above-mentioned second embodiment. 
The amount of the hydrolysis catalyst to be used is not specifically defined, generally falling between 0.0001 and 10 equivalents, but preferably between 0.001 and 1 equivalent in terms of acid, relative to the 1,1,3-trialkoxyalkane. 
If the amount of the catalyst used is smaller than 0.0001 equivalents, the hydrolysis speed will be low; but even if larger than 10 equivalents, such a large amount of the catalyst used could no more augment the intended effect. 
For the hydrogenation catalyst, herein usable are those used in the above-mentioned third embodiment. 
The amount of the hydrogenation catalyst to be used is not also specifically defined, generally falling between 0.01 and 50% by weight, but preferably between 0.1 and 20% by weight of the 3-alkoxyalkanal. 
If the amount of the catalyst used is smaller than 0.01% by weight, the hydrogenation speed will be low; but if larger than 50% by weight, it is unfavorable, since such a large amount of the catalyst used could no more augment the intended effect and the catalyst loss increases. 
The amount of water to be present in the reaction zone may well be equivalent or more relative to the 1,1,3-trialkoxyalkane, but is generally up to 20 equivalents.  If the amount of water is smaller than the equivalent thereto, the 1,1,3-trialkoxyalkane could not be hydrolyzed sufficiently; but if larger than 20 equivalents, it is unfavorable, since an additional step of post-treating the product for separating water from it will be needed and the step increases the energy costs for the method. 
The condition for simultaneous hydrolysis and hydrogenation in the process is not specifically defined.  In general, however, the temperature may fall between 20 and 250xc2x0 C., but preferably between 50 and 180xc2x0 C. If it is lower than 20xc2x0 C., the reaction speed will be low; but if higher than 250xc2x0 C., it is unfavorable, since the selectivity of the intended product, 3-alkoxyalkanol will lower. 
The hydrogen pressure may fall generally between 1 and 20 MPa, but preferably between 3 and 15 MPa.  If it is lower than 1 MPa, the reaction speed will be low; but even if higher than 20 MPa, such a high pressure could no more augment the intended effect.