Method for producing alkoxy-hydroxybenzaldehyde that is substantially free of alkyl-alkoxy-hydroxybenzaldehyde

1. A process for producing at least one alkoxyhydroxybenzaldehyde (“AHBA”), said process comprising forming at least one alkoxyphenol (“AP”) and at least one alkylalkoxyphenol (“AAP”) from at least one hydroxyphenol (“HP”) and separating (S) the AP from the AAP, said separating (S) being carried out prior to obtaining AHBA, wherein the AHBA is produced by addition of an aldehyde function to the AP by condensation with glyoxylic acid, followed by oxidation of the resulting compound, and wherein the separating (S) is carried out before the oxidation to give the AHBA compound.

2. The process as claimed in claim 1 , wherein the alkoxyhydroxybenzaldehyde (AHBA) is selected from vanillin (VA), ethylvanillin (EVA), and mixtures thereof.

3. The process as claimed in claim 2 , wherein the VA, EVA or mixtures thereof is substantially free of 5-methylvanillin (“MEVA”) and of 3-ethoxy-5-ethyl-4-hydroxybenzaldehyde (“EEVA”), wherein the AP is selected from guaiacol (GA), guaethol (GE) and mixtures thereof, and wherein the AAP is selected from 6-methylguaiacol (“MEGA”), 6-ethylguaethol (“2-ethoxy-6-ethylphenol” or “EGE”), and mixtures thereof.

4. The process as claimed in claim 1 , wherein the separating (S) is carried out before the reaction of AP with glyoxylic acid.

5. The process as claimed in claim 1 , wherein the separating (S) is carried out by one or more distillation steps.

6. The process as claimed in claim 1 , wherein the process further comprises

introducing a stream or fraction (E1) of a mixture M comprising guaiacol (GA), guaethol (GE), or mixtures thereof, denoted “G”, and 6-methylguaiacol (MEGA), 6-ethylguaethol (EGE), or mixtures thereof, denoted “AG”, in the presence of pyrocatechol (PC) in a distillation column (E),

recovering G essentially at the top of the distillation column in a stream or fraction (E2), and recovering PC and AG essentially at the bottom of the distillation column in a stream or fraction (E3).

7. The process as claimed in claim 6 , wherein the mixture M further comprises a dialkoxybenzaldehyde (DAB), and wherein DAB is recovered essentially at the bottom of the distillation column in the stream or fraction (E3).

8. The process as claimed in claim 6 , wherein PC represents from 25% to 75% by weight of the total weight of the stream or fraction (E1).

9. The process as claimed in claim 6 , wherein G represents from 25% to 75% by weight of the total weight of the stream or fraction (E1).

10. The process as claimed in claim 6 , wherein G represents more than 90% by weight of the total weight of the stream or fraction (E2), and wherein AG represents less than 1% by weight relative to the total weight of the stream or fraction (E2).

11. The process as claimed in claim 6 , wherein the stream or fraction (E2) comprises from 90% to 100% of G, from 0to 1% of AG, and from 0to 1% of VER, the percentages being expressed by weight relative to the total weight of the stream or fraction (E2).

12. The process as claimed in claim 6 , wherein PC represents more than 60% by weight of the total weight of the stream or fraction (E2), and wherein AG represents less than 8% by weight relative to the total weight of the stream or fraction (E3).

13. The process as claimed in claim 6 , wherein the stream or fraction (E3) comprises from 60% to 100% of PC, from 0to 8% of AG, and from 0 to 10% of VER, the percentages being expressed by weight relative to the total weight of the stream or fraction (E3).

14. The process as claimed in claim 6 , wherein the process further comprises distilling in a column (F) the stream or fraction (E3) from the bottom of the distillation column (E) by drawing off a stream or fraction (F6) at the side of the column (F) so as to draw off a stream or fraction enriched with PC.

15. A process for separating GA and/or GE from a mixture (M) comprising GA and/or GE and a 6-methylguaiacol (“MEGA”) and/or 6-ethylguaethol (“2-ethoxy-6-ethylphenol” or “EGE”) impurity, the process comprising introducing the mixture M into a distillation column in the presence of pyrocatechol (PC), recovering a stream or fraction comprising GA and/or GE at the top of the distillation column, and recovering a stream or fraction comprising PC, MEGA and/or EGE at the bottom of the distillation column.

16. A process for synthesizing at least one alkoxyphenol (“AP”) in the vapor phase, the process comprising forming at least one AP on the basis of an O-alkylation reaction in the vapor phase, between at least one hydroxyphenol (“HP”) and at least one O-alkylating agent, said reaction also forming at least one alkylalkoxyphenol impurity (“AAP”), said reaction thus forming a mixture M comprising AP, AAP and HP, introducing the mixture M into at least one distillation column, recovering a stream or fraction comprising AP at the top of the distillation column, recovering a stream or fraction comprising HP and AAP at the bottom of the distillation column, and optionally recycling the stream or fraction comprising AP downstream of the O-alkylation reaction and/or recycling the stream or fraction comprising HP upstream of the O-alkylation reaction.

17. The process as claimed in claim 16 , wherein the AP is selected from guaiacol (GA) and/or guaethol (GE), wherein the HP is pyrocatechol (“PC”), and wherein the AAP is selected from 6-methylguaiacol (“MEGA”) and/or 6-ethylguaethol (“2-ethoxy-6-ethylphenol” or “EGE”).