Lawyers for Salvatore F. DiMasi on Tuesday officially appealed his 2011 conviction on corruption charges, arguing federal prosecutors failed to prove that the disgraced former House speaker knowingly accepted kickbacks in exchange for wielding his political power.

In a petition more than 100 pages long, the lawyers argued that a US District Court judge failed to properly explain to jurors the definition of corruption laws: that prosecutors had to prove that DiMasi knowingly agreed to accept payments in exchange for acts he would take as House speaker, one of the most powerful positions in the state.

The lawyers also argued that US District Court Chief Judge Mark L. Wolf failed to explain to jurors that, under state law, politicians could accept gifts, but that gifts do not necessarily translate into bribes.

And, the lawyers also argued that Wolf erred in sentencing DiMasi to eight years in prison, calling it an unreasonably harsh sentence that was meant to unfairly punish DiMasi for deciding to go to trial, and for being the third consecutive House speaker convicted in federal court.

The lawyers argued that regardless of the outcome of the appeal on the case, “the matter should be remanded for sentencing.”

“DiMasi’s sentence was more than five times as long (as a co-defendant’s sentence) because he went to trial and publicly expressed his disagreement with the verdict,” the lawyers wrote in the petition to the US Court of Appeals for the First Circuit.

The petition is the beginning of what could be a lengthy legal process. Prosecutors must respond to DiMasi’s appeal and the appeals court could then consider the arguments.

DiMasi, now 67, was one of the most powerful politicians in Massachusetts before his conviction in June 2011 of honest service fraud and extortion. He is serving an eight-year sentence in a federal prison in North Carolina. He has been diagnosed with cancer since his incarceration.