Catalizzatore di Lindlar

Il catalizzatore di Lindlar, anche noto semplicemente come palladio Lindlar è un catalizzatore eterogeneo costituito da palladio deposto su carbonato di calcio ed avvelenato con varie forme di piombo, zolfo o chinolina. Viene utilizzato nell'idrogenazione degli alchini a dare alcheni (senza quindi giungere ad alcani), e prende il nome dal suo inventore Herbert Lindlar.

Preparazione

Esso è disponibile commercialmente ma può essere preparato riducendo il PdCl2 in uno slurry di carbonato di calcio aggiungendo poi acetato di piombo.[1][2] Molti altri agenti avvelenanti vengono utilizzati, tra cui PbO2 e la chinolina. Il contenuto di palladio è generalmente del 5% in peso.

Azione catalitica

Il catalizzatore viene utilizzato per l'idrogenazione di alchini ad alcheni (cioè senza ulteriore riduzione ad alcani). Il piombo serve a disattivare i siti attivi del palladio, ulteriormente deattivati con la chinolina o il 3,6-ditia-1,8-ottandiolo migliorandone così la selettività, impedendo la formazione di alcani. Pertanto, se un composto contiene un doppio legame ed un triplo legame, solo il triplo legame viene ridotto. Un esempio è la riduzione della fenilacetilene a stirene.

La reazione è stereoselettiva portando sempre al prodotto cis via syn (sin) addizione di idrogeno.[3] Esempi di una sua applicazione pratica sono la sintesi della vitamina A e della diidro vitamina K1.[4]

Note

  1. ^ Lindlar, H.; Dubuis, R., Palladium catalyst for partial reduction of acetylenes, in Organic Syntheses, vol. 46, 1966, DOI:10.15227/orgsyn.046.0089. URL consultato il 27 dicembre 2016.
  2. ^ (EN) H. Lindlar, Ein neuer Katalysator für selektive Hydrierungen, in Helvetica Chimica Acta, vol. 35, n. 2, 1º febbraio 1952, pp. 446–450, DOI:10.1002/hlca.19520350205. URL consultato il 27 dicembre 2016.
  3. ^ Overman, L. E.; Brown, M. J.; McCann, S. F., (Z)-4-(trimethylsilyl)-3-buten-1-ol, in Organic Syntheses, vol. 68, 1993, DOI:10.15227/orgsyn.068.0182. URL consultato il 27 dicembre 2016.
  4. ^ Fritz Weber, August Rüttimann "Vitamin K" Ullmann's Encyclopedia Of Industrial Chemistry, 2012, Wiley-VCH, Weinheim. DOI: 10.1002/14356007.o27_o08

Voci correlate

  Portale Chimica: il portale della scienza della composizione, delle proprietà e delle trasformazioni della materia

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