Lubricant Additives

262 Lubricant Additives: Chemistry and Applications

9.3.2.4 Mercaptan Route

Few producers synthesize sulfur carriers in a two-step process.

1. In the fi rst step, H 2 S is added to olefi ns under the catalytic action of Lewis acids. If strong
   activators such as BF 3 are used, the reaction takes place at as low as –20°C. Another pro-
   cedure works at 60–90°C. The resulting alkylmercaptans are distilled from the reaction
   mixture and isolated as intermediates (Equation 9.3). The nonreacted olefi ns are circulated
   back to the reaction vessel.

RHCCHR HS RHCCH(SH)R 2

Olefin

2

Alkylmercaptan

→ 


 (9.3)

2. The mercaptans are oxidized either with hydrogen peroxide (H 2 O 2 ) (Equation 9.4a) to the
   dialkyldisulfi des

2R H C 22 CH(SH) R H O 2 R H C CHR S S CHR CH R

Alkylmercaptan

 
 
 → 
 22 
 


 
 


DDialkyldisulfide

(9.4)

or by stoichiometric amounts of sulfur to trisulfi des (Equation 9.5) and polysulfi des (Equation 9.6)

22RHCCH(SH)R S RHCCHRSSSCHRCH R 2

Alkylmercaptan

 
 
 → 
 22 
 



 
 


DDialkylpolysulfide

HS 2 (9.5)

2 R H C 2 CH(SH) R Sx R H C CHR S (S ) S CH

Alkylmercaptan

 
 → 

 

 

2x
 1 RRCH R HS 22

Dialkylpolysulfide



(9.6)
This may be summarized in the reaction shown in Figure 9.7.
This process is mainly applied to olefi n-based sulfur carriers based on tri- and tetrapropyl-
ene as starting material because the resulting tertiary dodecylmercaptan may be used chemical
intermediate and in other applications such as rubber processing as.

9.3.3 OTHER SYNTHETIC ROUTES

9.3.3.1 Sulfurchlorination Route

Sulfur carriers can be synthesized in a two-step process using disulfur dichloride and sodium sul-
fi de solution (Figure 9.8). It had been widely used because it is a controlled way of adding discrete
S 2 -bridges to double bonds with little side reactions occurring.

FIGURE 9.7 Summary of two-step process.

+2 H 2 S

BF 3

+ 2 S

− H 2 S

2 2

− 20 °C

Tertiary dodecyltrisulfide

Tetrapropene

SH

S

S

S