## Facts

- Diane M. Dillon filed a patent application claiming hydrocarbon fuel compositions containing certain tetra-orthoester compounds and methods of reducing particulate (soot) emissions by adding those compounds to fuel.
- The examiner rejected multiple composition and method claims as obvious under 35 U.S.C. § 103 based on prior art disclosing structurally similar tri-orthoesters used as hydrocarbon fuel additives for dewatering (water scavenging).
- The Board of Patent Appeals and Interferences affirmed the obviousness rejection.
- A Federal Circuit panel initially reversed, but the court reheard the case en banc, vacated the panel decision, and reconsidered.
- Dillon argued the prior art did not suggest her discovered soot-reduction use and therefore could not support a prima facie case of obviousness.

## Issues

1. Whether a prima facie case of obviousness for chemical compounds/compositions requires both structural similarity and a prior-art suggestion or expectation of the same or similar utility/property as the claimed invention.
2. Whether Dillon’s fuel composition and method claims were obvious in view of prior art tri-orthoester fuel additives used for dewatering.

## Decision

- The en banc Federal Circuit affirmed the Board’s rejection of all challenged claims as obvious under § 103.
- The court held that a prima facie case of obviousness does not require a prior-art suggestion that the claimed compound has the same or similar usefulness as the applicant’s newly discovered property.
- The court found the prior art showed a close structural relationship between tri- and tetra-orthoesters and taught using orthoesters as fuel additives in the same field, supplying a reason to make and use the claimed compounds.
- The court concluded Dillon did not rebut the prima facie case with evidence of unexpected properties or other objective indicia sufficient to overcome obviousness.

## Legal Principles

- Prima facie obviousness in the chemical arts may be established by close structural similarity to prior art combined with a reason or motivation in the prior art to make or use the claimed subject matter in the relevant field.
- Prior art need not disclose or suggest the applicant’s newly discovered property or use to support a prima facie § 103 rejection.
- Properties and results remain part of the overall obviousness analysis, and an applicant may rebut a prima facie case with objective evidence such as unexpected results, superior properties, or other secondary considerations.
- If the applicant fails to produce persuasive rebuttal evidence, structurally similar compounds made for reasons suggested by the prior art are unpatentable as obvious even if a different advantage is later discovered.

## Conclusion

The Federal Circuit held that structural similarity and a reason to make/use the claimed chemical subject matter can establish prima facie obviousness without prior-art teaching of the same utility, and it affirmed the PTO’s rejection because Dillon did not show unexpected results or other objective evidence sufficient to overcome the prima facie case.


In re Dillon, 919 F.2d 688 (Fed. Cir. 1990) (en banc)