Process for making pure salicylic acid

{
  "publication_number": "US4137258A",
  "country": "US",
  "kind": "A",
  "title": "Process for making pure salicylic acid",
  "abstract": "Alkali metal salicylate can be efficiently acidified and the salicylic acid product formed contemporaneously sublimed by contacting the salicylate as a solid with gaseous hydrogen chloride at the conditions specified. The temperature of the gaseous hydrogen chloride is controlled so that the heat required to sublime the salicylic acid product is predominantly supplied by the heat of reaction of the hydrogen chloride with the alkali metal salt of the carboxylic acid.",
  "claims": [
    "1. A method of making salicylic acid of high purity comprising contacting sodium salicylate in the solid phase with a gas stream containing gaseous anhydrous hydrogen chloride so as to effect acidification of salicylic acid and contemporaneous sublimation of salicylic acid to a gas.",
    "2. The method as defined in claim 1 wherein the gas stream is maintained at a temperature in the range from about 90° C. to about 200° C.",
    "3. A method of making salicyclic acid of high purity from sodium salicylate in a continuous, two-step acidification process comprising the steps of: (a) in the first step, sodium salicylate in the solid phase is contacted at a reaction temperature below its softening point with a gas stream containing a greater than stoichiometric amount of gaseous, anhydrous hydrogen chloride to effect substantially complete acidification and the salicylic acid product is contemporaneously sublimed into the gas stream; (b) in the second step, the gas stream contacts a greater than stoichiometric amount of sodium salicylate in the solid phase at reactive conditions so as to effect acidification to the substantially complete exhaustion of the hydrogen chloride remaining in the gas stream, the salicylic acid product is contemporaneously sublimed and the unreacted sodium salicylate is cycled back to the first step.",
    "4. The method as defined in claim 3 wherein the sublimed salicylic acid product is condensed to a solid by means of a fine water spray controlled so as to effect transfer of heat contained in the gas stream into evaporation of the water without condensation."
  ],
  "description_excerpt": "This invention relates to the contemporaneous acidification of alkali metal salicylate and the sublimation of the salicyclic acid product.\n\nIt has long been known in the prior art that salicylic acid can be purified by sublimation. See, for example, U.S. Pat. Nos. 1,987,282 and 1,987,301. However, in the prior art the heat required to sublime the salicylic acid is supplied from external sources in a step separate and distinct from the acidification of the alkali metal salicylate.\n\nGenerally, the prior art acidifies sodium salicylate in a liquid medium containing a mineral acid to prepare salicylic acid. The liquid medium readily dissipates the heat of the acidification reaction. The salicylic acid is collected, dried and sublimed. The heat required to sublime the acid is imparted by a stream of heated gas or other means. The inefficiency of this heat transfer necessitates the use of relatively high temperatures which can decompose some of the salicylic acid.\n\nIn view of the deficiencies in the foregoing prior art methods of subliming salicylic acid, it would be highly desirable to provide a method of sublimation which utilizes the heat generated in the acidification of the alkali metal salicylate.\n\nThe FIGURE is a schematic flow diagram illustrating a specific embodiment of a multistep process relating to the acidification of sodium salicylate and the sublimation of the salicylic acid product.",
  "cpc": [
    "C07C 51/02",
    "C07C 51/43"
  ],
  "ipc": [
    "C07C 51/00",
    "C07C 51/02",
    "C07C 51/42",
    "C07C 51/43",
    "C07C 65/10",
    "C07C 67/00"
  ],
  "assignees": [
    "Dow Chemical Co"
  ],
  "inventors": [
    "Eugene R. Moore",
    "Roger L. Briggs",
    "David C. McDonald",
    "Richard Hoffman"
  ],
  "filing_date": "1978-04-07",
  "publication_date": "1979-01-30",
  "grant_date": "1979-01-30",
  "priority_date": "1978-04-07",
  "application_number": "US-89422278-A",
  "family_id": "25402774",
  "cited_by_count": 13,
  "citations": [
    "GB766887A",
    "US2891090A",
    "US3337616A",
    "US3359307A",
    "GB1201472A",
    "US3530174A",
    "JPS496304A"
  ]
}