Synthesis of N-Lauroyl Sarcosine by Amidocarbonylation: Comparing

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Synthesis of N-Lauroyl Sarcosine by Amidocarbonylation: Comparing Homogeneous and Heterogeneous Palladium Catalysts Sören Hancker, Stefanie Kreft, Helfried Neumann, and matthias Beller Org. Process Res. Dev., Just Accepted Manuscript • DOI: 10.1021/acs.oprd.7b00326 • Publication Date (Web): 14 Nov 2017 Downloaded from http://pubs.acs.org on November 14, 2017

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Organic Process Research & Development

Synthesis of N-Lauroyl Sarcosine by Amidocarbonylation: Comparing Homogeneous and Heterogeneous Palladium Catalysts Sören Hancker, Stefanie Kreft, Helfried Neumann and Matthias Beller* Leibniz-Institut für Katalyse e. V. an der Universität Rostock, Albert-Einstein-Straße 29a, 18059 Rostock, Germany.

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FOR TABLE OF CONTENTS ONLY


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KEYWORDS Amidocarbonylation, N-Lauroyl Sarcosine, Palladium Catalysis, N-Acyl Amino Acids.

ABSTRACT

An improved system for the synthesis of N-acyl amino acids via Pd-catalysed amidocarbonylation is reported. Utilising inexpensive Pd black gives the industrially important surfactant N-lauroyl sarcosine in excellent yields (95 %) on multi-g-scale. Advantages of the new system include reusability, decreased process temperature and importantly a drastically decreased co-catalyst loading.


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INTRODUCTION N-Acyl amino acids are of fundamental importance for chemistry and biology.1-5 In addition, they are of specific industrial interest as this class of compounds possesses a variety of different application fields. For example, pharmaceuticals such as Captopril or N-acetyl cysteine, food additives like Aspartame as well as surfactants such as N-lauroyl sarcosine (1) depict N-acyl amino acid derivatives as structural motives.4 The broad application range of amino acids as integral part of peptides as well as proteins and the importance of amino acid derivatives as building blocks for organic syntheses continue to attract the interest for more effective synthetic methodologies for their production.6, 7 Within the numerous possible syntheses for amino acids and their derivatives, the amidocarbonylation,8 also known as Wakamatsu reaction,9 displays an interesting approach due to the perfect atom efficiency. Complementary to the more common carbonylation reactions of olefins10-12 or aryl halides,13-15 this methodology employs readily accessible (in situ generated) aldehydes combined either with amides, nitriles, acetals or epoxides. While commercial routes for N-acyl amino acids, combining the Strecker reaction with subsequent

acylation,

produce

over-stoichiometric

amounts

of

salt

waste,

the

amidocarbonylation only results in the (co-)catalysts as “by-products”. Originally developed using Co2(CO)8 as catalyst,16-18 nowadays the palladium-catalysed methodology utilising lithium bromide and sulfuric acid as co-catalysts prevails in this area.19 Notably, this latter protocol further enhanced the substrate scope of the reaction.19-21


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Figure 1. Comparison of the industrial synthesis of N-lauroyl sarcosine and the amidocarbonylation pathway.

Due to the high foam-forming quality and good dermatological compatibility, long chain sarcosinates are of increasing interest as green detergents,4 which are produced in a quantity of 10 000 tonnes per year.8 As an example the commercial synthesis of N-lauroyl sarcosine is realised by reacting sarcosine with N-lauroyl chloride under Schotten-Baumann reaction conditions (Figure 1).4 Despite a decreased reactivity towards secondary amides, Lin and Knifton successfully synthesised N-lauroyl sarcosine in 95% overall yield employing 1 mol% of Co2(CO)8 and 200 bar CO/H2 at 120 °C via amidocarbonylation of N-methyl dodecanamide with paraformaldehyde (PFA).18 Further investigations by Hoechst AG gave the surfactant in a two staged pilot plant process.22, 23 While the amidocarbonylation theoretically incorporates every substrate atom in the product molecule, the Pd-catalysed procedure requires significant amounts of lithium bromide (35 mol%) and sulfuric acid (1 mol%) as co-catalysts.24, 25 Likewise, these additives were essential in the first reported heterogeneously catalysed amidocarbonylation using Pd/C.26 Herein, we describe an improved amidocarbonylation procedure using a novel heterogeneous Pd catalyst, which allowed to drastically reduce the lithium bromide loading to 2.5 mol%.


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RESULTS AND DISCUSSION Table 1. Comparison of various heterogeneous catalysts with PdBr2 for the model reaction.

Entrya

Catalyst

NMR-yieldb

1

PdBr2c

77

2

Pd black

52

3

Pd/C (ox.)

42

4

Pd/SiO2

48

5

Pd/Al2O3

22

6

Pd/N@Gr

48

7

Pd/Faujasite A 30

8

Pd/ZSM-5 A

9

Pd/Faujasite B

Synthesis of N-Lauroyl Sarcosine by Amidocarbonylation: Comparing

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