Selective O-alkylation of Phenol Using Dimethyl Ether

Round 1

Reviewer 1 Report

This work reports on a new synthetic route for anisole from phenol and dimethyl ether using heteropoly acid catalysts. The authors succeeded in synthesizing anisole with high selectivity using their acid catalysts. The authors characterized the catalysts by XRD, TEM, SEM-EDX, N2-isotherm, XPS and FT-IR. These results showed that the ’30 PTA’ catalyst had well-dispersed PTA with higher Lewis acid sites and lower Bronsted acid sites. The authors evaluated the catalytical performance of the prepared catalyst samples and showed that the ’30 PTA’ had good selectivity and reusability.  

However, there seems to be a lack of specific data on ‘eco-benign’ in the title. This process may not be zero-discharge process since methanol was produced as a by-product. I recommend the authors to calculate the e-factor in this process and compare it with those in other papers if the authors claim the process is eco-benign.

Other comment shown below.

p. 3, line 109

…, then dissolved in 40ml suitable alcohol…

Al2O3 powder is usually insoluble in most alcohol. If so, ‘dissolved’ may be fixed to ‘dispersed’.

p. 3, line 111

The pH of that solution ……

‘solution’ may be fixed to ‘slurry’ or ‘mixture’, if the situation is same as above.

p.3, line 126-

Experimental procedure

It is desirable to show procedure the authors used to calculate the conversion and selectivity.

p.4 Figure 1

The Miller indices of 37.07° and 45.89° for alumina shown in the figure 1 may not be correct.

p.5 Figure 5(a), 5(b) and 5(c)

Inconsistent titles for these figures.

5(a) 30PTA

5(b) O1s

5(c) γAl₂O₃

p. 9, line 235

… on γ-Al2O3 Fsupported catalyst…

‘Fsupported’ may be fixed to ‘supported’.

References

There seems to be any references that are not mentioned in the text.

Author Response

Separately attached

Author Response File: Author Response.pdf

Reviewer 2 Report

Mane et al. reported the synthesis of anisole from dimethyl ether (DME) and phenol over phosphotungstic acid (PTA) loaded γ-Al₂O₃ catalysts. DME was selected as an alkylating agent herein since the side product, methanol, can also take part in the reaction as a reactant to give higher conversions. The amounts of surface Lewis acid (LA) sites and Brönsted acid (BA) sites of catalysts were tuned by varying the PTA to γ-Al₂O₃ ratios during their preparation. Among catalysts tested, the 30 % PTA-impregnated γ-Al₂O₃ was found to be the most active catalyst with the highest selectivity towards anisole. The authors attributed this to the enhanced PTA dispersion and the greater amount of LA sites (cf. BA sites) on this sample. Although the result is interesting, some issues listed below must be addressed before I can recommend for publication.

[1] Page 6, Ln 176-179. The authors attributed the low surface area obtained for 40 PTA and 50 PTA to the covering of the active sites by excess PTA. It seems to me that PTA itself is the key active site based on the discussion below from the authors. Maybe the overall size of 40 PTA and 50 PTA is bigger (from the sharp XRD peaks of Keggin) due to the formation of the Keggin structure? Please also provide TEM or SEM images of these two samples.

 [2] Page 7, XPS section. Please at least include bare γ-Al₂O₃ as a control sample in Figures 5b and 5c for discussion. This may provide insight into the interplay between γ-Al₂O₃ and PTA at low surface concentrations.

 [3] Page 8, DRIFT section. Please elaborate the experimental details of this section (e.g., how DRIFT was conducted). Bare γ-Al₂O₃ should also be included in Figure 6 for comparison since surface Al³⁺ species is LA site (this material may also possess BA site in ultrasmall size). On the hand, the LA peak width of 40 PTA and 50 PTA is much broader than that of 20 PTA and 10 PTA. In my opinion, the sharp LA peak is due to the molecular form of surface PTA, while the widening of this LA peak may be closely associated with their aggregation (i.e., the formation of Keggin) in 40 PTA and 50 PTA. Please comment on this point.

 [4] Page 8, Ln 209-211. Bear in mind that surface hydroxyl groups may not necessarily be BA sites (see G. Busca/Catalysis Today 41 (1998) 191-206) especially for covalent oxides such as TiO₂ and ZnO. The sentences must be revised.

 [5] The authors would like to correlate the amount of LA/BA sites to the observed conversion and selectivity. However, no quantitative data was provided for an in-depth discussion. This could be approached by either the absorption coefficient of the corresponding IR bands (also see G. Busca/Catalysis Today 41 (1998) 191-206) or ammonia-TPD (temperature programmed desorption).

Author Response

Separately attached

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors have modified the manuscript appropriately. This improved manuscript seems to be useful in the field of O-alkylation of phenols using acid catalysts.

Reviewer 2 Report

I am happy with the response from the authors.