Quantitative assessment of alkyl chain branching in alcohol‐based surfactants by nuclear magnetic resonance

Abstract

Surfactants with branched hydrophobes have gained considerable interest, since these can be used in formulations for laundry cleaning at a wide range of conditions. The claims range from improved dissolution rate to hardness tolerance and stain removing efficacy. In contrast to the historically known heavily branched surfactants, novel branched surfactants are less compromised by increased biodegradability. These properties find their basis in the structural characteristics of the hydrophobe, such as number, position, and type of alkyl chain branches. Our current understanding of structure-property relations, however, is hampered by the lack of generic methodology needed to obtain structural data on hydrophobe branching. A nuclear magnetic resonance (NMR) approach was developed by which we could obtain a comprehensive set of quantitative hydrophobe branching parameters in alcoholbased surfactants. The 13 C and 1 H NMR spin systems of hydrophobe branched species were assigned by means of twodimensional NMR techniques. These assignments allowed the quantitative assessment of these branched species by straightforward signal integration in the 1 H and 13 C NMR spectra. The quantified NMR data can be used to understand product performance and the biodegradation of surfactants with branched hydrophobes.Paper no. S1451 in JSD 8, 73-82 (January 2005). KEY WORDS:Alcohol, alkyl chain, branching, feedstocks, hydrophobe branching, mid-chain branching, NMR, nuclear magnetic resonance spectroscopy.Since the switch by the industry from the poorly biodegradable, tetrapropylene-derived, and heavily-branched alkylbenzene sulfonates to the more quickly biodegradable linear alkylbenzene sulfonates (LAS) in the early 1960s, the surfactants used for laundry applications have differed mainly only in the type of hydrophilic group. Thus, the range of surfactant families available to the product developer has traditionally been limited to those based on sulfonates (LAS), carboxylates (soaps), sulfates, ethoxylates, or ethoxysulfates (1). In the last 10 yr, the range of hydrophiles has been extended even further, and new surfactants have come onto the market (2,3). With the exception of alkylbenzene-based materials, most surfactants are derived from olefins and alcoholbased materials that originate from petrochemical or oleochemical feedstocks. Until recently, there was limited room to maneuver with the hydrophobe structure. Alcohol feedstocks with branching at the β-position of the alkyl chain could be produced efficiently by the Oxo process, and they provided a good compromise between cleaning performance and biodegradability (5). In the conventional and modified Oxo processes (C-Oxo and M-Oxo, respectively), the degree of β-branching typically varies between 55 and 20%, respectively. Also, materials were available with high branching (HB) or random moderate branching (RMB) at the midchain positions of the alkyl chains, but owing to their unfavorable biodegradability, they were applicable only in niche applications. A rough overview of t...

Biodegradability of highly ethoxylated nonionic surfactants: Determination of intermediates and pathways of biodegradation

“…Nuclear magnetic resonance analysis ( 1 H and 13 C at 600 and 150 MHz, respectively) was conducted to confirm the extent of alkyl chain branching characteristics and the average EO length of the three nonionic samples [16]. The NMR samples were prepared by adding 10% of deuterated methanol (CD 3 OD, 99.8% deuteration; Sigma‐Aldrich, Steinheim, Germany).…”

Biodegradability of Highly Ethoxylated Nonionic Surfactants: Determination of Intermediates and Pathways of Biodegradation

“…The 1 H NMR spectra were recorded in 5-mm tubes, with a relaxation delay of 15 s. The NMR data sets were processed with the Bruker XWINNMR software (Ver 3.5; Bruker Biospin). By integration of the NMR signals of assigned structural elements [16], the branching characteristics, EO number, and free alcohol content could be obtained in a quantitative manner.…”

“…The average EO numbers, according to NMR, were lower than suggested (TO 20 ϭ 18 EO, AO 30 ϭ 23 EO, and AT 50 ϭ 40 EO). The branching features, as presented in Table 1, allow classification of hydrophobe type [16] and tentative assignment of the process technology to obtain the alcohol feedstock. The three samples represent three widely different types of alkyl chain branching and, thus, are of interest to study biodegradation behavior.…”

Synthesis and Characterization of Novel Surfactants Based on 2‐Hydroxy‐4‐(Methylthio)Butanoic Acid: 1. Anionic Surfactants

“…The most significant disadvantage of these surfactants as opposed to other anionic surfactants is their propensity to precipitate when divalent cations, e.g., calcium and magnesium, are present; in other words fatty-acid surfactants have inferior hardness tolerance. Numerous efforts have been made to understand how to formulate hardness tolerant detergents: for example hardness tolerant anionic surfactants [3][4][5][6][7][8][9][10][11][12][13][14][15], mixed surfactant systems [16][17][18][19], builders which capture hardness ions [2,20,21], and microemulsion based formulations insensitive to water hardness [2,22].…”

“…One well-utilized strategy to make hardness tolerant anionic surfactants is to add branches to the hydrophobic chain [3,13]. However, early attempts to produce hardness tolerant soaps such as highly-branched alkylbenzene sulfonates made from polypropylene failed because of poor biodegradability [23,24].…”