Cyclic ortho ester fuel additive

Abstract

The invention relates to liquid hydrocarbons containing cyclic ortho esters as dehydrating dehydrating icing inhibitors and to methods of using the compounds. The liquid hydrocarbons include fuels such aviation fuels, lubricants, hydraulic fluids and hydrocarbon solvents.

Claims

1. A liquid hydrocarbon comprising a dehydrating icing inhibitor selected from Formula I and Formula II, salts thereof or mixtures thereof; ##STR00006## where: R.sup.1 and R.sup.3 are independently selectable and are selected from a C.sub.1 to C.sub.6 substituted or non-substituted, branched or straight chain, alkyl or ether; R.sup.2 and R.sup.4 are independently selectable and are selected from a C.sub.1 to C.sub.7 substituted or non-substituted, straight or branched chain, alkyl; Y is independently selectable and is a substituted or non-substituted alkyl; y is an integer of 1 to 3; z is an integer of 2 to 6; and, wherein liquid hydrocarbon is a hydrocarbon fuel selected from an aviation fuel, gasoline, diesel and heating oil, a lubricant or a hydraulic fluid.

2. A liquid hydrocarbon according to claim 1, wherein the liquid hydrocarbon is a hydrocarbon fuel, lubricant, hydraulic fluid or hydrocarbon solvent.

3. A liquid hydrocarbon according to claim 2, wherein the hydrocarbon fuel is an aviation fuel, gasoline, diesel or heating oil.

4. A liquid hydrocarbon according to claim 1, wherein R.sup.1 and R.sup.3 are independently selected from CH.sub.3—, CH.sub.3CH.sub.2—, CH.sub.3O(CH.sub.2).sub.a—, where a is an integer of 1 to 5, and an alkylene glycol or polyalkylene glycol containing 1 to 6 carbon atoms.

5. A liquid hydrocarbon according to claim 4, wherein R.sup.1 or R.sup.3 are CH.sub.3CH.sub.2—.

6. A liquid hydrocarbon according to claim 1, wherein R.sup.2 and R.sup.4 are independently selected from —CH.sub.3, —CH.sub.2CH.sub.3, —CH.sub.2CH.sub.2CH.sub.3, —CH.sub.2CH(CH.sub.3).sub.2 and —CH.sub.2C(CH.sub.3).sub.3.

7. A liquid hydrocarbon according to claim 1, wherein R.sup.3 and R.sup.4 are independently selected and are methyl or ethyl.

8. A liquid hydrocarbon according to claim 1, wherein y is 2.

9. A liquid hydrocarbon according to claim 1, wherein Y is independently selected from —CH.sub.2— and —CH(CH.sub.3)—.

10. A liquid hydrocarbon comprising a dehydrating icing inhibitor selected from Formula I and Formula II, salts thereof or mixtures thereof; ##STR00007## where: R.sup.1 and R.sup.3 are independently selectable and are selected from a C.sub.1 to C.sub.6 substituted or non-substituted, branched or straight chain, alkyl or ether; R.sup.2 and R.sup.4 are independently selectable and are selected from a C.sub.1 to C.sub.7 substituted or non-substituted, straight or branched chain, alkyl; Y is independently selectable and is a substituted or non-substituted alkyl; y is an integer of 1 to 3; z is an integer of 2 to 6; where the dehydrating icing inhibitor has a Formula III or Formula IV or a salt thereof; ##STR00008## wherein R.sup.5 and R.sup.7 are hydrogen; and R.sup.6 and R.sup.8 are methyl, and wherein R.sup.6 and R.sup.8 may be cis or trans relative to each other.

11. A liquid hydrocarbon according to claim 1, comprising 0.01 to 2% by volume of the dehydrating icing inhibitor.

12. A liquid hydrocarbon according to claim 1, wherein the compound is formed from a 1,3-dioxolan-2-ylium salt.

13. A method of inhibiting ice crystal formation in a liquid hydrocarbon comprising mixing the liquid hydrocarbon with a compound selected from Formula I and formula II, or mixtures thereof: ##STR00009## where: R.sup.1 and R.sup.3 are independently selectable and are selected from a C.sub.1 to C.sub.6 substituted or non-substituted, branched or straight chain, alkyl or ether; R.sup.2 and R.sup.4 are independently selectable and are selected from a C.sub.i to C.sub.7 substituted or non-substituted, straight or branched chain, alkyl; Y is independently selectable and is a substituted or non-substituted alkyl; y is an integer of 1 to 3; z is an integer of 2 to 6.

14. A method according to claim 13, wherein 0.01 to 2% by volume of the dehydrating icing inhibitor(s) is added to the liquid hydrocarbon.

15. A method according to claim 13, wherein the liquid hydrocarbon is a hydrocarbon fuel, lubricant, or hydrocarbon solvent.

16. A method according to claim 15, wherein the hydrocarbon fuel is an aviation fuel, gasoline, diesel of heating oil.

17. A method according to claim 13, wherein R.sup.1 and R.sup.3 are independently selected from CH.sub.3—, CH.sub.3CH.sub.2—, —CH.sub.3O(CH.sub.2).sub.a—, where a is an integer of 1 to 5, and an alkylene glycol or polyalkylene glycol containing 1 to 6 carbon atoms.

18. A method according to claim 17, wherein R.sup.1 or R.sup.3 are CH.sub.3CH.sub.2—.

19. A method according to claim 13, wherein R.sup.2 and R.sup.4 are independently selected from —CH.sub.3, —CH.sub.2CH.sub.3, —CH.sub.2CH.sub.2CH.sub.3, —CH.sub.2CH(CH.sub.3).sub.2 and —CH.sub.2C(CH.sub.3).sub.3.

20. A method according to claim 13, wherein R.sup.3 and R.sup.4 are independently selected and are methyl or ethyl.

21. A method according to claim 13, wherein y is 2.

22. A method according to claim 13, wherein Y is independently selected from —CH.sub.2— and —CH(CH.sub.3)—.

23. A method of inhibiting ice crystal formation in a liquid hydrocarbon comprising mixing the liquid hydrocarbon with a compound selected from Formula I and formula II, or mixtures thereof: ##STR00010## where: R.sup.1 and R.sup.3 are independently selectable and are selected from a C.sub.1 to C.sub.6 substituted or non-substituted, branched or straight chain, alkyl or ether; R.sup.2 and R.sup.4 are independently selectable and are selected from a C.sub.1 to C.sub.7 substituted or non-substituted, straight or branched chain, alkyl; Y is independently selectable and is a substituted or non-substituted alkyl; y is an integer of 1 to 3; z is an integer of 2 to 6; wherein in dehydrating icing inhibitor has a Formula III or Formula IV or a salt thereof; ##STR00011## wherein R.sup.5 and R.sup.7 are hydrogen; and R.sup.6 and R.sup.8 are methyl, and wherein R.sup.6 and R.sup.8 may be cis or trans relative to each other.

24. A method of inhibiting ice crystal formation in a liquid hydrocarbon comprising mixing the liquid hydrocarbon with a 1,3-dioxolan-2-ylium salt.

25. A compound of Formula IV or a salt thereof; ##STR00012## where: R.sup.3 is independently selectable and is selected from a C.sub.1 to C.sub.6 substituted or non-substituted, branched or straight chain, alkyl or ether; R.sup.4 is independently selectable and is selected from a C.sub.1 to C.sub.7 substituted or non-substituted, straight or branched chain, alkyl; z is an integer of 2 to 6; R.sup.5 and R.sup.7 are hydrogen; and R.sup.6 and R.sup.8 are methyl, and wherein R.sup.6 and R.sup.8 may be cis or trans relative to each other as a dehydrating icing inhibitor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described by way of example only with reference to the following Figures:

(2) FIG. 1 shows a comparison of the relative rate constants (in parentheses) for the hydration of acetals 1-2, ketal 3 and ortho ester 4.

(3) FIG. 2 shows a typical chromatogram of GC analysis of jet fuel showing the complex mixture of components of Jet A-1.

(4) FIG. 3 Typical NMR spectra of TMOA in ACOM/AcONa buffer with TMS Salt.

(5) FIG. 4 Graph of kinetic data for reaction of TMOA with buffer D.

(6) FIG. 5 Calibration curve of water correlation and relative peak are (RPA) for ethanol by GC.

(7) FIG. 6 Kobs v [H+] for TMOA.

(8) FIG. 7 Fuel water partitioning and the implications for acid catalysed hydrolysis. The water scavenger is represented by a sphere.

(9) FIG. 8 The formation of 1,3,-dioxolan-2-ylium cations in water.

DETAILED DESCRIPTION OF SEVERAL EMBODIMENTS

(10) Acetals, ketals, ortho esters and cyclic ortho esters have been generally known in the art, such as the paper by Santry 1998 Supra, and may be obtained from a number of commercially available source such as Sigma Aldrich.

EXPERIMENTAL SECTION

Experimental GC

(11) The analyses were performed using an Agilent 5890 gas chromatograph equipped with a flame ionisation detector. The GC column used was of fused silica, HP-5MS, 30 m by 0.25 mm, with a helium flow rate of 1.5 mL/min. The temperature for the detector and injector was fixed at 250° C. The oven temperature used for the analysis was 80° C. for 4 minutes, then it was increased at 20° C./min to 240° C. and held for 2 minutes.

(12) Jet A-1, obtained by Air BP (Batch number BIS/HAL/12/035K), was dried by storing it over 3 Å molecular sieve for at least 24 hours. Standards with different water concentrations were prepared by adding measured volumes of distilled water by SGE μL syringes to 20 ml of anhydrous Jet A-1, taking extra care to inject the water in the middle of the solvent. Each standard was prepared just before use and ultrasonicated for 5 minutes to ensure an equal distribution of water.

(13) A reactant solution was prepared to enable a simple, one-step addition of all the necessary chemicals. This solution was prepared by mixing 10 mL of triethyl orthoformate (reagent), 1 mL of 3-methylpentane (internal standard) and 7.1 μL of methanesulfonic acid (catalyst) in a GC vial obtained from Supelco (Bellefonte, USA) Because of contamination from the atmospheric moisture, it was necessary to prepare a new reactant solution each day.

(14) For the analysis, 100 μL of reactant solution was added to 1 mL of a Jet A-1 sample in a 2 mL GC sample vial. To avoid water losses on the tip of the Gilson pipette used to measure the sample, the above mixture was used to rinse the tip of the pipette. All chemicals used in this experiment were purchased from Sigma Aldrich and, except the acid, distilled over anhydrous MgSO.sub.4 and kept over 3 Å molecular sieve. All sample vials were cleaned with acetone and dried at 200° C. for 2 hours.

Experimental NMR [25]

(15) Five buffers with constant acetic acid (AcOH) concentration and different H.sup.+ concentrations were made by varying the amount of sodium acetate (AcONa) added (see Table 1). As the ionic concentration of the solution has an impact on the rate constant of hydrolysis, sodium chloride was added to keep the ionic strength constant in all 5 buffers [26].

(16) TABLE-US-00001 TABLE 1 Buffer solutions in H.sub.2O Buffer [AcOH] [AcONa] [NaCl] A 0.192M 0.3947M 0.3693M B 0.192M 0.192M 0.572M C 0.192M 0.0658M 0.6982M D 0.192M 0.048M 0.716M E 0.192M 0.0185M 0.7455M

(17) The reaction samples were prepared directly in 5 mm NMR tube by adding 15 μL of TMOA in 500 μL of acetone-d6. To start the reaction 100 μL of acetic acid/sodium acetate aqueous buffer was added. All chemicals were purchased at the highest level of purity from Sigma Aldrich. Acetone-D6 and TMOA were dried before each experiment by distilling from 3 Å molecular sieve under nitrogen. Sodium chloride and sodium acetate were dried by heating them at T=100° C. for 4 hours under vacuum.

(18) A 300 MHz NMR spectrometer was used to follow the concentration of TMOA with time by acquiring nine sequential .sup.1H NMR spectra every 10 min (actual delay time=10.38 min). Presaturation solvent suppression technique was used to obscure the H.sub.2O signal. An external reference was used by adding to the NMR tube a sealed capillary tube with 3-(trimethylsilyl)-1-propanesulfonic acid sodium salt dissolved in D.sub.2O (concentration=0.1966 M).

(19) The TMOA .sup.1H NMR spectrum consists of two singlets resonating at 3.15 and 1.33 ppm, assigned to the —OCH.sub.3 and —CH.sub.3 residues, respectively (integrating 3:1—FIG. 7). The relative peak area (RPA—proportional to concentration) was measured by comparing the —CH.sub.3 resonance with that of the external reference. See FIG. 3.

(20) As an example, buffer D (pH=4.15) results are tabulated in Table 2 and they are represented in FIG. 4.

(21) TABLE-US-00002 TABLE 2 Kinetic data for reaction of TMOA with buffer D. Time (min) R.P.A. In R.P.A. 13.33 2.57 0.943906 23.71 2.47 0.904218 34.09 2.42 0.883768 44.47 2.24 0.806476 54.85 2.17 0.774727 65.23 2.08 0.732368 75.61 1.99 0.688135 85.99 1.9 0.641854 96.37 1.82 0.598837

Experimental Computational Study

(22) In order to calculate log K.sub.ow, two programs were used: KOWWIN™ and LogP (AB/LogP v2.0) from EPI suite and ACD/I-Lab, respectively [21, 22]. Both predict the log octanol-water partition coefficient by using an atom/fragment contribution method. The values reported in Table 2 are the averages of the two results.

(23) For estimation of mammalian and environmental toxicology, a series of programs with well-established computational methods were used. Water solubility and dermal permeability (kp) of a compound were determined through its K.sub.ow by WSKOWWIN™ and DERMWIN, respectively. MPBPWIN™ estimated the vapor pressure of these chemicals through their boiling points [21].

(24) The median lethal concentration (LC.sub.50) for Pimephales Promelas was calculated with ACD/I-Lab program [22].

(25) KOCWIN™ was used to predict carbon-normalized sorption coefficient for soil and sediment (K.sub.OC) by using two different models: the Sabljic molecular connectivity method with improved correction factors and the traditional method based on log K.sub.OW. Reported are the average values [21].

(26) BIOWIN™ estimates aerobic and anaerobic biodegradability of organic chemicals using 7 different models. We have only considered the ultimate biodegradation timeframe, achieved when a material is totally utilized by microorganisms, and the ready biodegradability prediction [21].

(27) Results & Discussion

(28) Removing Free Water from Jet Fuel: Proof of Concept

(29) Because of the complexity of Jet A-1, there is a relatively narrow window of “visibility” in a GC chromatogram to observe analytical markers before the components of Jet A-1 begin to elute (<2 min at the conditions reported in the experimental section) (FIG. 2). A careful choice of methodology was therefore necessary before work could be undertaken in order to demonstrate the feasibility of using ortho esters as a dehydrating agents for jet fuel.

(30) Chen et al. developed a useful analytical approach for measuring the water content of a range of hydrophobic solvents such as decane; a reasonable surrogate for jet A-1 [16]. The method relies upon the indirect determination of water via the GC measurement of ethanol (EtOH), a volatile side-product liberated via the acid-catalysed stoichiometric reaction of water with ortho ester 5 (Scheme 1).

(31) ##STR00003##

(32) The GC method was adapted for measuring water in jet fuel (see experimental). Importantly—and as confirmed by GC-MS—the products of the hydrolysis of 5 i.e., ethanol, ethyl formate 6, in addition to the internal standard (3-methylpentane) elute before the components of jet fuel (FIG. 2). The retention times for ethanol and 3-methylpentane (internal standard) were 1.69 and 1.8 min, respectively.

(33) For each water standard, the relative peak area (RPA) of ethanol was calculated by dividing the ethanol peak area by the internal standard peak area. To correct for atmospheric and residual water present in the reactant solution, the RPA of the reactant solution was subtracted from each ethanol RPA. A calibration curve was plotted, and is presented in FIG. 5.

(34) As can be seen, an excellent linear correlation (R.sup.2=0.9995%) exists between the ethanol RPA and water concentration in Jet A-1 in the concentration range examined (100-1250 ppm v/v).

(35) In conclusion, the linearity of this relationship clearly illustrates the effectiveness of using triethyl orthoformate 5 as a dehydrating agent for Jet A-1. Importantly, the GC method reported here can be used to determine water concentrations in jet fuel beyond the accuracy of the industry standard—namely the Karl Fischer method [16].

(36) As discussed in the introduction, jet fuel is mildly acidic, and indeed the batch of Jet A-1 used for these analyses is reported to be 0.01 mg KOH/g by ASTM D3242 [17]. In order to examine the capacity of 5 to dehydrate jet fuel in the absence of added acid, the GC method described here was repeated without methane sulfonic acid. In the absence of an added acid catalyst—with only the inherent acidity of jet fuel to catalyse the process—the reaction was found to be 60-75% complete after 2 days, compared to 100% completion in 30 minutes using methane sulfonic acid. Since a strong acid catalyst is undesirable inside the fuel tank of an aircraft, a kinetically faster process must be sought either through modifying the; (a) reaction conditions i.e., the nature of the acid catalyst, or (b) molecular structure of the ortho ester.

(37) The Nature of the Acid Catalyst, and its Relationship to the Rate of Hydrolysis

(38) Although there is still much to be uncovered about the acid catalysed hydrolysis of ortho esters, it is generally accepted that the process can be divided into two stages; namely, the formation of the water scavenging dialkoxy carbenium ion 11 from ortho ester 7, and the subsequent hydration and collapse of 11 to afford ester 13 (Scheme 2). The initial protonation of 7, and the subsequent formation of 11 is considered to be slow—and therefore rate determining—whereas the hydration of 11 and all subsequent steps en route to 13, are considered to be relatively fast [18, 19].

(39) The protonation of 7, and the subsequent formation of 11 is subject to two clearly defined mechanisms; namely general (via undissociated acid HA)—and specific (via dissociated acid H.sup.+) acid catalysis (Scheme 2) [18]. In the case of the former, H-A delivers a proton to an oxygen atom of the ortho ester, which then eliminates a molecule of alcohol ROH—via 10—to give 11 with and overall velocity constant k.sub.HA. The cation is rapidly hydrated and ultimately collapses to ester 13 through several steps, and the ultimate elimination of a second molecule of ROH. In the case of specific acid catalysis, dissociated H.sup.+ protonates the ortho ester 7 to afford—via 10—dialkoxy carbenium ion 11 with overall velocity constant k.sub.H+. The fate of hydrated 11 is the same for both mechanistic pathways. It is clear therefore that the overall rate for the process observed in Scheme 2 will be dependent upon the slower of the two mechanistic pathways.

(40) ##STR00004##

(41) General acid catalysis is ordinarily facilitated by weaker, undissociated acids; conversely specific acid catalysis tends to be facilitated by stronger, fully dissociated acids. However, for all but the strongest acids both pathways will be operative. Given the physical environment in which we expect a water scavenger to operate—namely within the fuel tank of an aircraft—we sought to optimise the reaction velocity using the weakest acid possible. It was necessary therefore to determine the magnitude of the velocity constants associated with the simultaneous processes k.sub.H+ and k.sub.HA.

(42) As mentioned earlier, jet fuel is mildly acidic. In the presence of polar solvents, such as water, the extent of the acid dissociation will be proportional to the acid dissociation constant (K.sub.a) of the individual acids present (Eq. II).

(43) $\begin{array}{cc}{K}_a=\frac{\left[H^{+}\right]\left[A^{-}\right]}{\left[\mathrm{HA}\right]}& \left(\mathrm{II}\right)\end{array}$

(44) The approach adopted for determining k.sub.H+ and k.sub.HA, was to exploit the constancy of K.sub.a (=1.75×10.sup.−5 mol/L) whilst varying the numerators (i.e., [A.sup.−] 2.fwdarw.0.1 and pH 5.07.fwdarw.3.74) and maintaining [HA] constant (i.e., 0.192 mol/L). As the overall rate of reaction (equation III) is a summation of both processes described by k.sub.H+ and k.sub.HA, the rate constant k.sub.obs is therefore proportional to the concentration of both associated and dissociated acids (equation IV).
rate=k.sub.obs[R—C(OR).sub.3]  (III)
k.sub.obs=k.sub.H+[H.sup.+]+k.sub.HA[HA]  (IV)

(45) Given that [HA] is constant, expression IV becomes equivalent to that of a straight line and k.sub.H+ and k.sub.HA may be determined by plotting k.sub.obs vs [H.sup.+]. To obtain k.sub.obs however, the rate equation integrated over time (Eq. V) must be used [14].
In[R—C(OR).sub.3].sub.t—In[R—C(OR).sub.3].sub.0=−k.sub.obst  (V)

(46) .sup.1H NMR spectroscopy is the technique of choice when studying processes which occur on this timescale. Our choice of HA was acetic acid (AcOH), and five buffered solutions with different H.sup.+ concentration were prepared by varying the amount of sodium acetate (AcONa=A.sup.−). For the study, we switched focus from the aldehyde derivative TEOF (5, Scheme 1) used for the proof of concept study to the faster reacting keto-derivative trimethyl orthoacetate (TMOA) 8, Scheme 2 where R=—CH.sub.3) for reasons of atom economy (20% lighter). For each buffered solution (see experimental) a k.sub.obs was obtained and the results presented in Table 3 and FIG. 5.

(47) TABLE-US-00003 TABLE 3 Experimentally determined k.sub.obs [AcOH]/[AcONa] [H.sup.+] (mol/L) K.sub.obs (min.sup.−1) 0.486 8.51 × 10.sup.−6 1.6 × 10.sup.−3 1 1.75 × 10.sup.−5 2.4 × 10.sup.−3 2.918 5.11 × 10.sup.−5 3.6 × 10.sup.−3 4 7.00 × 10.sup.−5 4.2 × 10.sup.−3 10.378 1.82 × 10.sup.−4 .sup. 8 × 10.sup.−3

(48) From these data, k.sub.obs v. [H.sup.+] may be plotted (FIG. 5) and a straight line fitted (y=35.464×+1.6×10.sup.−3; R.sup.2=0.993) from which values for the gradient of the slope and y-intercept afford k.sub.H+=35.5 min.sup.−1 and, k.sub.HA=7.8×10.sup.−3 min.sup.−1 respectively. It is clear that the pathway catalysed by dissociated acid H.sup.+ (specific acid catalysis—scheme 2) is approximately 4500 times faster than the pathway catalysed by undissociated AcOH, within the pH range studied here (3.7.fwdarw.5.0).

(49) The significant difference in the experimentally determined rate constants for the hydrolysis of an ortho ester by both dissociated H.sup.+ and associated HA acids has important implications for the partitioning behaviour of a scavenger across the fuel-free water interface (FIG. 7). Associated—relatively weak—acids (HA) tend to reside in the apolar environment of jet fuel, unlike the hydrophilic hydroxonium cation which by definition prefers the polar environment of free water. Our stated objective is to design a water scavenger (S) which preferentially partitions into the lipophilic fuel phase (i.e., K.sub.ow=[S].sub.octanol/[S].sub.water>0, FIG. 7)—which in the case of an ortho ester means that here, it may only undergo a slow hydrolysis reaction with dissolved water—thereby ensuring fuel protection. However, at the phase boundary with free water, the water scavenger may encounter dissolved dissociated acid H.sup.+ and subsequently undergo a rapid hydrolysis reaction—thereby consuming free water.

(50) Dual Purpose Water Scavengers

(51) Cyclic ortho esters such as 14a-e (Scheme 3) present themselves as exciting, dual purpose agents because upon hydrolysis with water, the five membered ring (remembering atom economy) cleaves to afford hydrophilic alcohols of type 15a-e which incorporate as many sites for hydrogen bonding as the de-icer di-EGME (Scheme 3). Through manipulation of the substituent —R (14, Scheme 3, and Table 1) it is possible to fine-tune the lipophilicity of the water scavenger to ensure that it partitions preferentially into the fuel phase (i.e., consistent with K.sub.ow>0). In order for the corresponding alcohol 15 produced by the hydrolysis of 14 to express de-icing properties it must be sufficiently hydrophobic to partition preferentially into residual free water (K.sub.ow<0) [20]. There will clearly be a tipping point for the ideal dual-reagent as the lipophilicity of 14 and hydrophobicity of 15 as substituent —R varies through the series a.fwdarw.e.

(52) ##STR00005##

(53) The commonly accepted measure of lipophilicity, log K.sub.ow [20] was calculated for compounds 14a-e and 15a-e, and the average values derived from two computational models are presented in Table 4 [21, 22]. Ethanol has experimentally and calculated log K.sub.ow values of −0.31 and −0.09, respectively [21-23].

(54) TABLE-US-00004 TABLE 4 Calculated log K.sub.ow for cyclic ortho esters 14a-e and acyclic alcohols 15a-e. R 14 15 a —CH.sub.3 +0.97 −0.55 b —CH.sub.2CH.sub.3 +1.41 −0.05 c —CH.sub.2CH.sub.2CH.sub.3 +1.78 +0.42 d —CH.sub.2CH.sub.2CH.sub.2CH.sub.3 +2.33 +0.84 e —CH.sub.2CH.sub.2CH.sub.2CH.sub.2CH.sub.3 +2.88 +1.54

(55) As expected, when —R becomes progressively lipophilic down the series a.fwdarw.e, log K.sub.ow becomes increasingly positive which is consistent with favourable partitioning in fuel. Therefore it is anticipated that the series 14a-e possesses partitioning behaviour consistent with an effective water scavenger. However, in the case of the alcohols 15a-e, preferential partitioning in water is clearly indicated for 15a-b and 15c must be considered to be at the tipping-point for Jet fuel. Other structures may be used for other liquid hydrocarbons having different components.

(56) In conclusion, calculations suggest that ortho esters 14a-c present themselves as water scavengers whose corresponding hydrolysis products 15a-e possess potential dual-action de-icing activity. In the next section, an evaluation of the mammalian and environmental toxicology of 14/15a-c is made.

(57) Human and Environmental Toxicology

(58) Well established computational methods (i.e., US EPA and ACD/I-La) have been used here to estimate and compare the human and environmental toxicity of 14/15a-c, and di-EGME [21, 22]. The results of these calculations are presented in Table 5; we compare estimated values for di-EGME because experimentally determined values for 13/14a-c are unavailable.

(59) TABLE-US-00005 TABLE 5 Calculated human and environmental toxicological evaluations of di-EGME and 14/15a-c. 15 14 Compounds Di-EGME a b c a b c Water solubility   1 × 10.sup.6   1 × 10.sup.6 4.1 × 10.sup.5 1.4 × 10.sup.5 4.6 × 10.sup.3 1.5 × 10.sup.3 5.1 × 10.sup.2 (mg/L, 25° C.) Vapour 1.1 × 10.sup.−1 1.5 × 10.sup.−1 1.7 × 10.sup.−1 5.2 × 10.sup.−2  4.8  1.8 6.9 × 10.sup.−1 Pressure (mmHg, 25° C.) Dermal 5.4 × 10.sup.−5 1.6 × 10.sup.−4 2.9 × 10.sup.−4 5.1 × 10.sup.−4 2.9 × 10.sup.−3 5.1 × 10.sup.−3   9 × 10.sup.−3 Permeability Kp (cm/hr) LC.sub.50 (mg/L) for 9.9 × 10.sup.3 3.1 × 10.sup.3 1.5 × 10.sup.3 9.2 × 10.sup.2 4.2 × 10.sup.3 3.4 × 10.sup.3 2.7 × 10.sup.3 Pimephales Promelas Soil Adsorption 7.4 × 10.sup.−1 1.15 1.72 3.13 16.2 33.7 58.6 Coefficient K.sub.oc (L/kg) Ultimate weeks days- weeks weeks weeks- weeks- weeks- biodegradation weeks month month month timeframe Ready yes yes yes yes no no no biodegradability prediction

(60) Water solubility, vapour pressure, and dermal permeability were evaluated as potential measures of worker and consumer exposure. The median lethal concentration (LC.sub.50) for Pimephales promelas was used to evaluate aquatic toxicity. Biodegradation, soil adsorption—along with water solubility—were used to estimate the environmental fate of compounds, and ultimately exposure to the general population.

(61) In the first instance we will compare the calculated toxicity of de-icers 15a-c with di-EGME (Table 5). Both di-EGME and 15a-c are quite soluble in water—the former more so. As K.sub.p tends to increase with increasing lipophilicity, the inverse trend observed for water solubility would appear to be reflected in the greater dermal permeability of 15a-c. The vapour pressure of di-EGME and 15a-b are very similar—thereby posing similar risks to workers. The aquatic toxicities (LC.sub.50) of 15a-b are of the same order of magnitude as di-EGME indeed all of the compounds in Table 3 fall well below the criteria for aquatic toxicity (i.e., >100 mg/L) [24]. Di-EGME and 15a-c are all weakly sorbing compounds K.sub.oc<25 L/kg); importantly 15a-c are more likely than Di-EGME to adhere soil, and thereby not contribute to runoff.

(62) The corresponding water scavengers 14a-c are relatively lipophilic compared to di-EGME, and as one would expect, possess greater dermal permeabilities, and their vapour pressures are also greater, posing marginally greater risk to workers. However, because 14a-c are dual-action agents, it is likely that the effective concentration required for jet fuel will be less than di-EGME—as will the ultimate level of exposure to workers. Ortho esters 14b-c in particular possess strong sorbing properties, and are less likely to contribute to runoff. Although ready biodegradability for 13a-c is not predicted, this does not take into account the likelihood that acidic soils will catalyze hydrolysis to 15a-c.

CONCLUSIONS

(63) We have established that ortho esters are effective dehydrating agents for jet fuel. We have developed an analytical method—based upon the rapid hydrolysis of ortho esters—for determining the concentration of water in jet fuel. Detailed kinetic measurements using .sup.1H NMR spectroscopy have established that ortho esters are rapidly hydrolysed by dissociated acid catalysts, whilst a slower process occurs with an associated acid catalyst. The implications for the development of a water scavenger are that lipophilic ortho esters will hydrolyse slowly in jet fuel, yet rapidly at the interface with free water. Cyclic ortho esters offer the potential for dual-purpose reagents which, upon hydrolysis, afford de-icers. Candidate substrates have been identified based upon their calculated partitioning behaviour and their human and environmental profiles have been assessed with respect to di-EGME.

REFERENCES

(64) 1. Coordinate Research Council, Technical Report no. 635, Handbook of Aviation Fuel Properties, 3.sup.rd edition, 2004. 2. Baena, S., Lawson, C. and Lam, J. K.-W., “Dimensional Analysis to Parameterise Ice Accretion on Mesh Strainers.” SAE Technical Paper 2011-01-2795, 2011, doi:10.4271/2011-01-2795. 3. Chevron Corporation, Technical Review, Aviation Fuels Technical Review, 2006. 4. Baena-Zambrana, S., Repetto, S. L., Lawson, C. P. and Lam, J. K.-W., “Behaviour of water in jet fuel-A literature review.” Progress in Aerospace Sciences, 2013, doi:10.1016/j.paerosci.2012.12.001. 5. Ministry of Defence, Defence Standard 91-91, Turbine Fuel Aviation Kerosine Type, Jet A-1. Issue 6, 2008. 6. Carpenter, M. D., Hetherington, J. L., Lao, L., Ramshaw, C. et al., “Behaviour of Water in Aviation Fuels at Low Temperatures.” Presented at IASH 2011, USA, Oct. 16-20, 2011. 7. Lao, L., Ramshaw, C., Yeung, H., Carpenter, M. et al., “Behavior of Water in Jet Fuel Using a Simulated Fuel Tank.” SAE Technical Paper 2011-01-2794, 2011, doi:10.4271/2011-01-2794. 8. Taylor, S. E., “Component Interactions in Jet Fuels: Fuel System Icing Inhibitor Additive.” Energy & Fuels 22(4):2396-2404, 2008. 9. Trohalaki, S., Pachter, R. and Cummings, J. R., “Modeling of Fuel-System Icing Inhibitors.” Energy & Fuels 13(5):992-998, 1999. 10. Mushrush, G. W., Beal, E. J., Hardy, D. R., Hughes, J. M. and Cummings, J. C., “Jet Fuel System Icing Inhibitors: Synthesis and Characterization.” Industrial & Engineering Chemistry Research 38(6):2497-2502, 1999. 11. Sittig, M., “Handbook of Toxic and Hazardous Chemicals and Carcinogens.” Noyes Publications, New Jersey, 1985. 12. Meshako, C. E., Bleckmann, C. A., and Goltz, M. N., “Biodegradability and Microbial Toxicity of Aircraft Fuel System Icing Inhibitors.” Environmental Toxicology 14(4):383-390, 1999. 13. Mushrush, G. W., Stalick, W. M., Beal, E. J., Bash, S. C. et al., “The Synthesis of Acetals and Ketals of the Reduced Sugar Mannose as Fuel System Icing Inhibitors.” Petroleum Science and Technology 15(3&4):237-244, 1997. 14. Atkins, P. W., “Physical Chemistry.” 2.sup.nd edition, Oxford University Press, Oxford, UK, 1982. 15. Deslongchamps, P., Dory, I. L., and Li, S., “The Relative Rate of Hydrolysis of a Series of Acyclic and Six-Membered Cyclic Acetals, Ketals, Ortho esters and Orthocarbonates.” Tetrahedron 56(22)3533-3537, 2000. 16. Chen, J. and Fritz, J. S., “Gas-Chromatographic Determination of Water after Reaction with Triethyl Orthoformate.” Analytical Chemistry 6(18):2016-2020, 1991. 17. SGS Oil, “Jet A1 Full Test Report. Test Certificate No:AV12-00033.001.” SGS UK Ltd, Bristol, UK, 2012. 18. Cordes, E. H. and Bull, H. G., “Mechanism and Catalysis for Hydrolysis of Acetals, Ketals, and Ortho Esters.” Chemical Reviews 74(5):581-603, 1974. 19. Wenthe, A. M. and Cordes, E. H., “Concerning the Mechanism of Acid-Catalyzed Hydrolysis of Ketals, Ortho Esters, and Orthocarbonates.” Journal of the American Chemical Society 87(14):3173-3180, 1965. 20. Chang, J. H., Beal E. J., Stalick, W. M. and Mushrush, G. W., “Fuel System Icing Inhibitors: the Synthesis of Esters of Oxaacids.” Petroleum Science and Technology 16(9&10):979-1000, 1998. 21. US EPA, Estimation Programs Interface Suite™ for Microsoft® Windows (version 4.11), United States Environmental Protection Agency, Washington, USA, 2013. 22. ACD/I-Lab2 Predictor (version 5.0.0.184), Advanced Chemistry Development, Inc., Toronto, Canada, 2013. 23. Hansch, C., Leo, A. and Hoekman, D., “Exploring QSAR: Hydrophobic, Electronic, and Steric Constants.” American Chemical Society, Washington, USA, 1995. 24. US EPA, “Estimating Aquatic Toxicity with ECOSAR.” http://www.epa.gov/opot/sf/pubs/ecosar.pdf, 2013. 25. Ports, R. A. and Schaller, R. A., “Kinetics of the Hydrolysis of Orthoesters: A General Acid-Catalyzed Reaction.” Journal of Chemical Education 70(5):421-424, 1993. 26. Bunton C. A. and Reinheimer, J. D., “Electrolyte Effects on the Hydrolysis of Acetals and Ortho Esters.” Journal of Physical Chemistry 74(26):4457-4464, 1970.