The present invention provides a method for industrially producing a highly pure aromatic nitrile compound and a highly pure aromatic carboxylic acid compound safely and highly efficiently at low costs. Compound (2) is subjected to Willgerodt reaction in the presence of an additive as necessary, and the obtained amide compound (3) is hydrolyzed and neutralized to give carboxylic acid compound (4). Carboxylic acid compound (4) is reacted with a halogenating agent in the presence of a catalyst as necessary in an organic solvent, and further reacted with an amidating agent, and the obtained amide compound (5) or (6) is reacted with a dehydrating agent to give nitrile compound (1). Alternatively, carboxylic acid compound (4) is reacted with a halogenating agent and a compound represented by the formula R.sup.6SO.sub.2R.sup.7 in the presence of a catalyst as necessary in an organic solvent to give nitrile compound (1). Np is a naphthyl group optionally having substituent(s), R.sup.5 is an alkylene group having 1-3 carbon atoms, and other symbols are as described in the DESCRIPTION. ##STR00001##

The present invention provides a method for industrially producing a highly pure aromatic nitrile compound and a highly pure aromatic carboxylic acid compound safely and highly efficiently at low costs. Compound (2) is subjected to Willgerodt reaction in the presence of an additive as necessary, and the obtained amide compound (3) is hydrolyzed and neutralized to give carboxylic acid compound (4). Carboxylic acid compound (4) is reacted with a halogenating agent in the presence of a catalyst as necessary in an organic solvent, and further reacted with an amidating agent, and the obtained amide compound (5) or (6) is reacted with a dehydrating agent to give nitrile compound (1). Alternatively, carboxylic acid compound (4) is reacted with a halogenating agent and a compound represented by the formula R.sup.6SO.sub.2R.sup.7 in the presence of a catalyst as necessary in an organic solvent to give nitrile compound (1). Np is a naphthyl group optionally having substituent(s), R.sup.5 is an alkylene group having 1-3 carbon atoms, and other symbols are as described in the DESCRIPTION. ##STR00001##

The present invention provides a method for industrially producing a highly pure aromatic nitrile compound and a highly pure aromatic carboxylic acid compound safely and highly efficiently at low costs. Compound (2) is subjected to Willgerodt reaction in the presence of an additive as necessary, and the obtained amide compound (3) is hydrolyzed and neutralized to give carboxylic acid compound (4). Carboxylic acid compound (4) is reacted with a halogenating agent in the presence of a catalyst as necessary in an organic solvent, and further reacted with an amidating agent, and the obtained amide compound (5) or (6) is reacted with a dehydrating agent to give nitrile compound (1). Alternatively, carboxylic acid compound (4) is reacted with a halogenating agent and a compound represented by the formula R.sup.6SO.sub.2R.sup.7 in the presence of a catalyst as necessary in an organic solvent to give nitrile compound (1). Np is a naphthyl group optionally having substituent(s), R.sup.5 is an alkylene group having 1-3 carbon atoms, and other symbols are as described in the DESCRIPTION. ##STR00001##

The invention relates to an industrially viable and advantageous process for the preparation of (2S,3R)-2-amino-3-(3,4-dihydroxyphenyl)-3-hydroxypropanoic acid, having the following formula (I) generally known as Droxidopa, or of intermediates useful in the synthesis thereof.

##STR00001##

The invention relates to an industrially viable and advantageous process for the preparation of (2S,3R)-2-amino-3-(3,4-dihydroxyphenyl)-3-hydroxypropanoic acid, having the following formula (I) generally known as Droxidopa, or of intermediates useful in the synthesis thereof.

##STR00001##

The present invention provides a method for industrially producing a highly pure aromatic nitrile compound and a highly pure aromatic carboxylic acid compound safely and highly efficiently at low costs. Compound (2) is subjected to Willgerodt reaction in the presence of an additive as necessary, and the obtained amide compound (3) is hydrolyzed and neutralized to give carboxylic acid compound (4). Carboxylic acid compound (4) is reacted with a halogenating agent in the presence of a catalyst as necessary in an organic solvent, and further reacted with an amidating agent, and the obtained amide compound (5) or (6) is reacted with a dehydrating agent to give nitrile compound (1). Alternatively, carboxylic acid compound (4) is reacted with a halogenating agent and a compound represented by the formula R.sup.6SO.sub.2R.sup.7 in the presence of a catalyst as necessary in an organic solvent to give nitrile compound (1). Np is a naphthyl group optionally having substituent(s), R.sup.5 is an alkylene group having 1-3 carbon atoms, and other symbols are as described in the DESCRIPTION.

##STR00001##

The present invention provides a method for industrially producing a highly pure aromatic nitrile compound and a highly pure aromatic carboxylic acid compound safely and highly efficiently at low costs. Compound (2) is subjected to Willgerodt reaction in the presence of an additive as necessary, and the obtained amide compound (3) is hydrolyzed and neutralized to give carboxylic acid compound (4). Carboxylic acid compound (4) is reacted with a halogenating agent in the presence of a catalyst as necessary in an organic solvent, and further reacted with an amidating agent, and the obtained amide compound (5) or (6) is reacted with a dehydrating agent to give nitrile compound (1). Alternatively, carboxylic acid compound (4) is reacted with a halogenating agent and a compound represented by the formula R.sup.6SO.sub.2R.sup.7 in the presence of a catalyst as necessary in an organic solvent to give nitrile compound (1). Np is a naphthyl group optionally having substituent(s), R.sup.5 is an alkylene group having 1-3 carbon atoms, and other symbols are as described in the DESCRIPTION.

##STR00001##

The present invention provides a method for industrially producing a highly pure aromatic nitrile compound and a highly pure aromatic carboxylic acid compound safely and highly efficiently at low costs. Compound (2) is subjected to Willgerodt reaction in the presence of an additive as necessary, and the obtained amide compound (3) is hydrolyzed and neutralized to give carboxylic acid compound (4). Carboxylic acid compound (4) is reacted with a halogenating agent in the presence of a catalyst as necessary in an organic solvent, and further reacted with an amidating agent, and the obtained amide compound (5) or (6) is reacted with a dehydrating agent to give nitrile compound (1). Alternatively, carboxylic acid compound (4) is reacted with a halogenating agent and a compound represented by the formula R.sup.6SO.sub.2R.sup.7 in the presence of a catalyst as necessary in an organic solvent to give nitrile compound (1). Np is a naphthyl group optionally having substituent(s), R.sup.5 is an alkylene group having 1-3 carbon atoms, and other symbols are as described in the DESCRIPTION.

##STR00001##

The present invention provides a method for producing an aromatic nitrile compound, the method comprising a dehydration reaction wherein a desired compound can be selectively obtained with high yield while suppressing the generation of by-products during the regeneration of an aromatic amide compound into the corresponding aromatic nitrile compound. In addition, the present invention realizes a method for efficiently producing a carbonate ester by applying the abovementioned production method to a method for producing a carbonate ester. The above are achieved by means of a method for producing an aromatic nitrile compound involving a dehydration reaction wherein an aromatic amide compound is dehydrated, the method having a contact step for bringing the aromatic amide compound into contact with a catalyst in a gas phase during the dehydration reaction.

The present invention provides a method for producing an aromatic nitrile compound, the method comprising a dehydration reaction wherein a desired compound can be selectively obtained with high yield while suppressing the generation of by-products during the regeneration of an aromatic amide compound into the corresponding aromatic nitrile compound. In addition, the present invention realizes a method for efficiently producing a carbonate ester by applying the abovementioned production method to a method for producing a carbonate ester. The above are achieved by means of a method for producing an aromatic nitrile compound involving a dehydration reaction wherein an aromatic amide compound is dehydrated, the method having a contact step for bringing the aromatic amide compound into contact with a catalyst in a gas phase during the dehydration reaction.