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OPINION Reactions ShareShare onFacebookTwitterWechatLinked InRedditEmail C&EN, 2021, 99 (31), p 3August 30, 2021Cite this:C&EN 99, 31, 3Letters to the editorHydrogen fluorideIn the Aug. 24, 2020, issue of C&EN, a two-page feature article by Michael McCoy was published on “a new route to hydrogen fluoride” with the subheadline “In a first for the US, the fluorochemical raw material will be made from a fertilizer industry by-product” (page 24). While I agree that this is a very worthwhile undertaking to utilize an environmental pollutant for supplying an important raw material for fluorochemical makers, the article omitted important information on the history of this process. The concept of using the SiF4 by-product from fertilizer plants as a source of HF and using it as a starting material for the synthesis of fluorocarbons is neither new nor a first for the US. It was developed 60 years ago in the US at Stauffer Chemical in Richmond, California, by Albert Mohr. The Mohr process was utilized to prepare either concentrated HF or SiF4 and was reduced to practice on the pilot-plant scale. It is described in detail in US patent 3,257,167, issued on June 21, 1966.Furthermore, the use of SiF4 to produce fluorochemicals was extensively studied in the early ’60s at Stauffer and is described in US patent 3,287,426 by Attila Pavlath and me, issued on Nov. 22, 1966, and in the publication “Silicon Tetrafluoride, a New Fluorinating Agent” (J. Org. Chem. 1964, DOI: 10.1021/jo01033a052). The use of SiF4 for producing hydrohalocarbon and halocarbon compounds has also been patented by Bamidele Omotowa in 2009 in the world patent WO 2009/032849 A1.Karl O. ChristeCalabasas, CaliforniaFrank DavisAs a former graduate student of Frank Davis in the biochemistry department at Rutgers University, I appreciated your commemorating his invention of attaching polyethylene glycol to proteins to escape the body’s immune response (May 31, 2021, page 13).Before this work he was a nucleic acid chemist who discovered pseudouridine, the most abundant modification in RNA (J. Biol. Chem.1957, 227, 907).Philip BarnettNew York CityTitanium dioxide in foodThis letter is in response to the article on titanium dioxide in foodpublished in C&EN’s May 17, 2021, issue (page 13).I cannot think of any cogent reason for permitting any purely cosmetic additive in food unless it is a natural constituent of some other foodstuff generally recognized as safe. In my opinion, all artificial food colorings should be banned and the public should be educated to recognize, accept and—ultimately—prefer foods with their natural appearance.Alexander MoreLondon CorrectionAug. 16/23, 2021, page 38: The Talented 12 profile of Chern-Hooi Lim incorrectly says he raised $7 million for his company, New Iridium. The company has raised $2.5 million in nondilutive funding.