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Synthesis 2017; 49(09): 1931-1937
DOI: 10.1055/s-0036-1588746
short review
© Georg Thieme Verlag Stuttgart · New York

Silica Gel Stabilized Na and Na/K Alloys: Highly Effective, Versatile and Environmentally Friendly Reducing Agents

Massimo Carraro
Department of Chemistry and Pharmacy, University of Sassari, Via Vienna 2, 07100 Sassari, Italy   Email: ugo@uniss.it
,
Luisa Pisano
Department of Chemistry and Pharmacy, University of Sassari, Via Vienna 2, 07100 Sassari, Italy   Email: ugo@uniss.it
,
Ugo Azzena*
Department of Chemistry and Pharmacy, University of Sassari, Via Vienna 2, 07100 Sassari, Italy   Email: ugo@uniss.it
› Author Affiliations
Further Information

Publication History

Received: 27 January 2017

Accepted after revision: 21 February 2017

Publication Date:
23 March 2017 (online)

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Abstract

Na and Na/K alloys in the liquid phase can be absorbed into amorphous silica gel at loadings up to 40 wt%. Further heating of these so-called stage 0 materials at 150 or 400 °C furnishes stage I and stage II materials, respectively, as free-flowing powders that can be handled under much safer conditions than the corresponding starting materials. Stage I Na and Na2K possess valuable reducing properties and they have found a variety of low impact applications in organic synthesis, including, e.g., the reductive deprotection of several functional groups, the development of safer protocols to operate the Bouveault–Blanc and the Birch reductions, and a new and particularly efficient approach to the Grignard and Darzens reactions.

1 Introduction

2 Reductive Deprotection Procedures

3 Bouveault–Blanc Reduction of Esters

4 Ammonia-Free Birch Reductions

5 Synthesis of Alkyldiaryl- and Dialkylarylphosphines

6 C–C Bond Forming Reactions

7 Further Applications

8 Conclusion

Key words

alkali metal - sodium - potassium - silica gel - reduction - electron transfer - green chemistry - low impact
 

  • References

  • 1 Armour MA. Hazardous Laboratory Chemicals Disposal Guide . 3rd ed. Lewis Publishers; Boca Raton: 2003: 484 and 535
    CrossrefSearch in Google Scholar
  • 3 Products from SiGNa Chemicals are internationally marketed by different suppliers. More information is available on the company website at: http://www.signachem.com. Retrieved 26/01/2017.
  • 4 Dye JL, Cram KD, Urbin SA, Redko MY, Kackson JE, Lefenfeld M. J. Am. Chem. Soc. 2005; 127: 9338
    CrossrefPubMedSearch in Google Scholar
  • 5 As a note of caution, it was reported that prolonged exposure of stage I materials to laboratory air caused a loss of their reducing power, most probably as a function of ambient humidity levels. Accordingly, it is usually recommended to test the efficiency of M-SG(I) by measuring the amount of H2 evolved upon reaction with EtOH. See also refs. 19 and 22.
  • 6 Dye JL, Nandi P, Jackson JE, Lefenfeld M, Bentley PA, Dunyak BM, Kwarcinski FE, Spencer CM, Lindman TN, Lambert P, Jacobson PK, Redko MY. Chem. Mater. 2011; 23: 2388
    CrossrefSearch in Google Scholar
  • 7 Shatnawi M, Paglia G, Dye JL, Cram KC, Lefenfeld M, Billinge SJ. L. J. Am. Chem. Soc. 2007; 129: 1386
    CrossrefPubMedSearch in Google Scholar
  • 8 Pittalis M, Azzena U, Pisano L. Tetrahedron 2013; 69: 207 ; and references therein
    CrossrefSearch in Google Scholar
  • 10 Nandi P, Redko MY, Petersen K, Dye JL, Lefenfeld M, Vogt PF, Jackson JE. Org. Lett. 2008; 10: 5441
    CrossrefPubMedSearch in Google Scholar

      • Formation of ring-opening byproducts during the reductive deprotection of N-sulfonylaziridines is a known reaction. For an investigation of the deprotection of a variety of N-tosylaziridines with sodium naphthalenide and anthracenide in ethereal solvents, see:
    • 11a Bergmeier SC, Seth PP. Tetrahedron Lett. 1999; 40: 6181 ; and references therein
      CrossrefSearch in Google Scholar
    • 11b Bellos K, Stamm H, Speth D. J. Org. Chem. 1991; 56: 6846
      CrossrefSearch in Google Scholar
  • 12 Nandi P, Dye JL, Jackson JE. Tetrahedron Lett. 2009; 50: 3864
    CrossrefSearch in Google Scholar
  • 13 For a discussion of the factors affecting the alkali-metal-mediated reductive cleavage of benzylic carbon–heteroatom bonds, see: Azzena U, Dettori G, Pisano L. Curr. Org. Chem. 2011; 15: 1006 ; and references therein
    CrossrefSearch in Google Scholar
  • 14 Maurya CK, Gupta PK. Tetrahedron Lett. 2015; 56: 2228 ; and references therein
    CrossrefSearch in Google Scholar
  • 16 Bodnar BS, Vogt PF. J. Org. Chem. 2009; 74: 2598 ; and references therein
    CrossrefPubMedSearch in Google Scholar

      • Another non-pyrophoric sodium-dispersion (Na-D15, Na particle size 5–15 μm), commercialized by Pentagon Fine Chemicals Ltd., was successfully applied to the reduction of a broad range of aliphatic esters to primary alcohols in the presence of a moderate excess (4.5 equiv) of i-PrOH in a hydrocarbon solvent:
    • 17a An J, Work DN, Kenyon C, Procter D. J. Org. Chem. 2014; 79: 6743
      CrossrefPubMedSearch in Google Scholar

      • More recently, it was reported a highly efficient synthesis of α,α-dideuterio alcohols by the reduction of carboxylic acid esters with a 40% Na dispersion in mineral oil, employing hexane as a solvent and EtOH-d 1 as a deuterium source:
    • 17b Han M, Ma X, Yao S, Ding Y, Yan Z, Adijiang A, Wu Y, Li H, Zhang Y, Lei P, Ling Y, An J. J. Org. Chem. 2017; 82: 1285
      CrossrefSearch in Google Scholar
  • 18 Reaction of esters with Na metal in the absence of an added proton donor leads to the formation of products of acyloin condensation. See, for example: Makosza M, Grela K. Synlett 1997; 267
    Thieme Connect
  • 19 Hook JM, Mander LN. Nat. Prod. Rep. 1986; 3: 35 ; and references therein
    CrossrefSearch in Google Scholar
  • 20 The National Institute for Occupational Safety and Health recommend an exposure limit of 25 ppm, 8 h time-weighted average: Gangopadhyay RK, Das SK. Process Saf. Prog. 2008; 27: 15
    CrossrefSearch in Google Scholar
  • 21 Nandi P, Dye JL, Jackson JE. J. Org. Chem. 2009; 74: 5790
    CrossrefPubMedSearch in Google Scholar
  • 22 Costanzo MJ, Patel MN, Petersen KA, Vogt PF. Tetrahedron Lett. 2009; 50: 5463
    CrossrefSearch in Google Scholar
  • 23 Abourahma H, Bradley L, Lareau NM, Reesbeck M. J. Chem. Educ. 2014; 91: 443
    CrossrefSearch in Google Scholar
    • 24a Nandi P, Dye JL, Bentely P, Jackson JE. Org. Lett. 2009; 11: 1689 ; and references therein
      CrossrefPubMedSearch in Google Scholar
    • 24b Lefenfeld M, Dye JL, Nandi P, Jackson JE. WO 2008131270, 2008
  • 25 Schlosser M In Organometallics in Synthesis, a Manual . Schlosser M. Wiley; New York: 1994. 1. and references therein
    CrossrefSearch in Google Scholar
  • 26 Chou TS, Tsao CH, Hung SC. J. Organomet. Chem. 1986; 312: 53
    CrossrefSearch in Google Scholar
  • 27 Layman WJ. Jr, Welsh GW. US 5,866,720, 1999
  • 28 Kapoor M, Hwu JR. Sci. Rep. 2016; 6: 36225
    CrossrefPubMedSearch in Google Scholar
  • 29 The recovered epoxycoumarins exhibited significant anti-hepatitis C virus activities, see ref. 24
  • 30 Jackson JE, O’Brien BN, Kedzior SK, Fryz GR, Jalloh FS, Banisafar A, Cladwell MA, Braun MB, Dunyak BM, Dye JL. Tetrahedron Lett. 2015; 56: 6227
    CrossrefSearch in Google Scholar
  • 31 Maurya CK, Mazumder A, Kumar A, Gupta PK. Synlett 2016; 27: 409 ; and references therein
    CrossrefPubMedSearch in Google Scholar
  • 32 Sengupta D, Basu B. Tetrahedron Lett. 2013; 54: 2277
    CrossrefSearch in Google Scholar
  • 33 Mandal B, Basu B. RSC Adv. 2014; 4: 13854
    CrossrefSearch in Google Scholar
  • 34 Marvel CS, Bailey WJ, Inskeep GE. J. Polym. Sci. 1946; 1: 275
    CrossrefSearch in Google Scholar
  • 35 Ito M, Carlotti S, Deffieux A, Lefenfeld M. WO 20090459 14, 2009
  • 36 Sartbaeva A, Wells SA, Sommariva M, Lodge MJ. T, Jones MO, Ramirez-Cuesta AJ, Li G, Edwards PP. J. Cluster Sci. 2010; 21: 543
    CrossrefSearch in Google Scholar
  • 37 Ogilvie AD, Makepeace JW, Hore K, Ramirez-Cuesta AJ, Apperley DC, Mitchels JM, Edwards PP, Sartbaeva A. Chem. Phys. 2013; 427: 61
    CrossrefSearch in Google Scholar
  • 38 https://www.epa.gov/greenchemistry/presidential-green-chemistry-challenge-winners; retrieved 26/01/2017.